#55

**本番 DB のバックアップをかならずすること**

Reviewed-on: #420
Co-authored-by: miteruzo <miteruzo@naver.com>

AGENTS.md

@@ -124,7 +124,7 @@ npm run preview
 - For arrays, never put whitespace or a line break immediately before `]`.
 - Keep the first element on the same line as `[` by default.
 - If an array would exceed the line limit, break after `[` and indent
-  elements by 4 spaces.
+  elements 4 spaces deeper than the statement's base indentation.
 
 ### Ruby delimiter and wrapping rules
 
@@ -140,6 +140,32 @@ npm run preview
   99 文字を超えるなら block 形式へ切り替へるか、message 定数化などで縮める。
 - Ruby の method chain や call argument を折り返す際、call-site の `)` を
   block close のやうに独立させない。
+- Ruby では、行末の `\` を用途を問はず一切使用しない。
+- Ruby では、文字列連結、logger message、method call、条件式、SQL 断片、
+  正規表現その他すべての式で、行末バックスラッシュによる継続を禁止する。
+- Ruby の block body は、その基準位置から 2 空白深くする。
+- Ruby の wrapped expression、method argument、array element、hash pair などの
+  continuation indentation は、その statement の基準位置から 4 空白深くする。
+- Ruby の continuation indentation を、行頭からの絶対空白数として扱はない。
+- Ruby では、暗黙的に継続可能な構文を優先し、method call、array、Hash 及び
+  括弧内ではバックスラッシュなしで改行する。
+- Ruby では、行長制限を守るために行末バックスラッシュを導入してはならない。
+- Ruby で行末バックスラッシュが必要に見える場合は、括弧内で自然に改行する、
+  一つの文字列補間へまとめる、中間変数へ分ける、`format` を使ふ、heredoc を
+  使ふ、array 又は Hash を組み立ててから処理する、条件式全体を括弧で囲む、
+  method へ抽出する、のいづれかへ書き換へる。
+- Ruby では、一つの文字列を、改行をまたいだ隣接文字列 literal として記述しない。
+- Ruby では、method argument 内でも、複数の文字列 literal を区切りなしで縦に
+  並べない。
+- RSpec の `describe`、`context`、`it` 等の description が長い場合は、意味を
+  保ったまま一行へ収まる文言へ短縮する。
+- 文字列を短縮できない場合は、用途に応じて `format`、heredoc 又は中間変数を
+  検討する。
+- ただし RSpec description では、原則として簡潔な一行の文字列を使ふ。
+- formatter 又は自動修正にも、Ruby の行末バックスラッシュを生成させない。
+- 新規 code だけでなく、今回触れる Ruby code にも行末バックスラッシュを残さない。
+- 例へば class body 内の array は、class body の 2 空白を基準に、更に 4 空白
+  深くするため、結果として行頭から 6 空白になる。
 
 Bad:
 
@@ -191,6 +217,63 @@ end
 
 Bad:
 
+```rb
+Rails.logger.info(
+    "post_import_metadata_fetch_failure "\
+    "#{ payload.to_json }")
+```
+
+Good:
+
+```rb
+payload = {
+    error: e.class.name,
+    message: e.message }
+
+Rails.logger.info(
+    "post_import_metadata_fetch_failure #{ payload.to_json }")
+```
+
+Bad:
+
+```rb
+message = "first "\
+          "second"
+```
+
+Good:
+
+```rb
+message = format(
+    '%<first>s %<second>s',
+    first: 'first',
+    second: 'second')
+```
+
+Bad:
+
+```rb
+result = first_value + \
+         second_value
+```
+
+Bad:
+
+```rb
+it(
+    'returns 409 when stale changes '
+    'do not conflict'
+) do
+```
+
+Good:
+
+```rb
+it 'returns mergeable 409 for stale non-conflicting changes' do
+```
+
+Bad:
+
 ```rb
 records.each {
   do_work(_1) }
@@ -225,20 +308,37 @@ records.each {
   formatting as the local reference shape: component and callback bodies use
   2-space block indentation, single-line bodies do not gain unnecessary
   braces, wrapped expressions use 4-space continuation indentation, multi-
-  stage ternaries use explicit parentheses, and only complete leading runs
-  of 8 spaces are compressed to tabs.
-- In TypeScript and TSX only, tabs are for leading 8-column compression only.
+  stage ternaries use explicit parentheses, and TypeScript / TSX indentation
+  and alignment whitespace compress every complete run of 8 spaces to tabs.
 - A tab does not represent one indentation level.
-- Do not replace 2-space or 4-space indentation with tabs.
-- First determine visible indentation using 2-space block indentation and
-  4-space continuation indentation, then compress only complete leading runs
-  of 8 spaces into tabs.
-- Tabs are only for leading indentation, never for spaces after non-space
-  text.
-- Keep residual leading 2, 4, or 6 spaces after any tab compression.
+- In TypeScript and TSX, first determine visible indentation using 2-space
+  block indentation and 4-space continuation indentation, then compress every
+  complete run of 8 spaces used for indentation or column alignment to tabs.
+- In TypeScript and TSX, 8-space compression is mandatory, not optional.
+- In TypeScript and TSX, this applies both to leading indentation and to
+  alignment whitespace after non-space text, such as aligned inline type
+  columns.
+- In TypeScript and TSX, keep residual 2, 4, or 6 spaces after each tab
+  compression.
+- In TypeScript and TSX, do not treat a tab as one logical indentation level.
+- In TypeScript and TSX, do not alter string literals, template-literal
+  contents, regular expressions, or user-facing text merely to apply tab
+  compression.
 - Examples: 2 columns = 2 spaces, 4 columns = 4 spaces, 6 columns = 6
   spaces, 8 columns = 1 tab, 10 columns = 1 tab + 2 spaces, 12 columns = 1
-  tab + 4 spaces, 16 columns = 2 tabs.
+  tab + 4 spaces, 14 columns = 1 tab + 6 spaces, 16 columns = 2 tabs.
+- When TypeScript or TSX code already uses column alignment, apply the same
+  8-space compression rule to that alignment whitespace.
+- Example:
+
+```ts
+type Props = {
+    row:	      PostImportRow
+    displayNumber?:   number
+    onEdit?:	  () => void
+    onRetry?:	  () => void
+    onToggleSkip?:    (checked: boolean) => void }
+```
 - TypeScript and TSX imports may stay on one line if they remain within the
   line limit; do not expand short type-only imports mechanically.
 - Keep runtime value imports and type imports in separate declarations.
@@ -474,8 +574,32 @@ and layout reuse, follow `frontend/AGENTS.md`.
   wording and placement before implementing it.
 - Do not invent replacement copy when removing unrequested wording.
 - Do not create, modify, or run tests unless the user explicitly asks for
-  test work. When the user asks for tests, keep working and rerun them until
-  they pass or the remaining failure is clearly blocked.
+  test work. When the user asks for tests, keep working within the permitted
+  test-file scope and rerun them until they pass or the remaining failure is
+  clearly blocked.
+- Test-only work includes adding, updating, deleting, reorganising, or fixing
+  SyntaxError in tests. During test-only work, do not modify production code.
+- During test-only work, do not change production constants, behaviour, API
+  contracts, validation, routes, authentication, permissions, UI, copy,
+  dependencies, limits, thresholds, defaults, migrations, schema, or
+  environment settings to satisfy tests.
+- Do not make production code match failing tests, mock assumptions, fixtures,
+  snapshots, old expectations, or stale setup. This includes changing
+  production constants merely because a test expects a different value.
+- If test work reveals a production bug, spec mismatch, or missing behaviour,
+  stop without modifying production code and report: the failing test or
+  discovered issue, the related production file, the actual behaviour, the
+  expected behaviour, and why a production change appears necessary.
+- Modify production code for test failures only when the user explicitly asks
+  for that production change. Do not expand a test task into a production task
+  on your own authority.
+- If the user explicitly asks for both production implementation and test
+  updates, implement production code to the confirmed specification first,
+  then add or update tests to verify that specification. Never roll production
+  behaviour back to satisfy old tests.
+- If it is unclear whether the test or the production implementation is stale,
+  or a test cannot be corrected without changing production code, ask the user
+  instead of guessing.
 
 ## Backend rules
 
@@ -598,10 +722,10 @@ and layout reuse, follow `frontend/AGENTS.md`.
   beginning of a line.
 - The TSX-specific self-review must confirm JSX closing markers and closing
   parentheses keep the surrounding compact style.
-- The TypeScript/TSX self-review must confirm leading block indentation uses
-  2 spaces per level, wrapped continuations use the repository's 4-space
-  continuation alignment, and complete leading runs of 8 spaces may be
-  compressed to tabs.
+- The TypeScript/TSX self-review must confirm block indentation uses 2 spaces
+  per level, wrapped continuations use the repository's 4-space continuation
+  alignment, and every complete run of 8 spaces used for indentation or
+  alignment has been compressed to tabs.
 - Prefer `const` arrow functions for TypeScript/TSX component and helper declarations.
 - Put two blank lines before and after top-level `const` function
   declarations, unless imports, exports, or file boundaries make that awkward.
@@ -614,9 +738,18 @@ and layout reuse, follow `frontend/AGENTS.md`.
 - Indent the block body 2 spaces deeper than the keyword and opening brace.
 - Put the closing `}` on its own line at the same indentation as the keyword.
 - Do not write `try {`, `catch {`, or `finally {`.
-- In TypeScript and TSX, convert every complete leading run of 8 spaces to a
-  tab character.
-- A leading tab is exactly equivalent to 8 leading spaces.
+- In TypeScript and TSX, convert every complete run of 8 spaces used for
+  indentation or alignment to a tab character.
+- In TypeScript and TSX, a tab is exactly equivalent to 8 columns, whether it
+  appears at the beginning of a line or in alignment whitespace after
+  non-space text.
+- In TSX, JSX nesting uses 2-space block indentation and wrapped JSX
+  attributes use 4-space continuation indentation; after visible columns are
+  determined, compress every complete run of 8 spaces in the resulting
+  indentation or alignment to tabs.
+- In TSX, do not leave JSX subtree indentation at 8, 10, 12, 14, or 16
+  columns as spaces alone; convert each complete run of 8 spaces to tabs and
+  keep only the residual 2, 4, or 6 spaces.
 - In TypeScript and TSX function declarations, including `const` arrow
   function declarations, classify the parameter list before placing the closing
   `)`.
@@ -1259,9 +1392,9 @@ to `.ts` and `.tsx`:
 7. JSX `>` and `/>` stay with the final prop unless nearby code proves
    otherwise.
 8. JSX closing parentheses keep the compact local style.
-9. Leading block indentation uses 2 spaces per level, wrapped continuations
-   use the repository's 4-space continuation alignment, and complete leading
-   runs of 8 spaces may be compressed to tabs.
+9. Block indentation uses 2 spaces per level, wrapped continuations use the
+   repository's 4-space continuation alignment, and every complete run of 8
+   spaces used for indentation or alignment has been compressed to tabs.
 10. No line has trailing whitespace.
 
 Preferred:

backend/app/controllers/application_controller.rb

@@ -85,4 +85,13 @@ class ApplicationController < ActionController::API
                    base_errors: },
            status:
   end
+
+  def normalise_json value
+    return nil if value.nil?
+    return JSON.parse(value) if value.is_a?(String)
+
+    value
+  end
+
+  def resolve_locale! = Locale.find_by(code: params[:locale]) || Locale.nipponese
 end

backend/app/controllers/deerjikists_controller.rb

@@ -1,5 +1,7 @@
 class DeerjikistsController < ApplicationController
   def show
+    locale = resolve_locale!
+
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
     return render_bad_request('platform は必須です．') if platform.blank?
@@ -7,10 +9,10 @@ class DeerjikistsController < ApplicationController
 
     deerjikist = Deerjikist
                  .joins(:tag)
-                 .includes(tag: :tag_name)
+                 .includes(tag: :tag_names)
                  .find_by(platform:, code:)
     if deerjikist
-      render json: DeerjikistRepr.base(deerjikist)
+      render json: DeerjikistRepr.base(deerjikist, language_code: locale.language_code)
     else
       head :not_found
     end
@@ -20,6 +22,7 @@ class DeerjikistsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
     tag_id = params[:tag_id].to_i
@@ -32,7 +35,7 @@ class DeerjikistsController < ApplicationController
       d.save!
     end
 
-    render json: DeerjikistRepr.base(deerjikist)
+    render json: DeerjikistRepr.base(deerjikist, language_code: locale.language_code)
   end
 
   def destroy

backend/app/controllers/gekanator_posts_controller.rb

@@ -2,7 +2,7 @@ class GekanatorPostsController < ApplicationController
   def index
     posts =
         Post
-        .preload(:post_similarities, tags: :tag_name)
+        .preload(:post_similarities, tags: :tag_names)
         .with_attached_thumbnail
         .order(Arel.sql(
             'COALESCE(posts.original_created_before - INTERVAL 1 MINUTE, ' \
@@ -56,7 +56,7 @@ class GekanatorPostsController < ApplicationController
   def tag_json tag
     {
       id: tag.id,
-      name: tag.name,
+      name: tag.name('ja'),
       category: tag.category
     }
   end

backend/app/controllers/gekanator_questions_controller.rb

@@ -126,9 +126,9 @@ class GekanatorQuestionsController < ApplicationController
     end
 
     Tag
-        .joins(:tag_name)
+        .joins(:tag_names)
         .where(category: categories.uniq)
-        .where(tag_names: { name: names.uniq })
+        .where(tag_names: { language_code: 'ja', primary_flg: true, name: names.uniq })
         .where.not(deprecated_at: nil)
         .pluck('tags.category', 'tag_names.name')
         .each_with_object({ }) do |(category, name), h|

backend/app/controllers/materials_controller.rb

@@ -7,6 +7,8 @@ class MaterialsController < ApplicationController
   rescue_from MaterialZipExporter::MissingFileError, with: :render_zip_missing_file
 
   def index
+    locale = resolve_locale!
+
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
 
@@ -20,7 +22,7 @@ class MaterialsController < ApplicationController
     q = Material.includes(:material_export_items,
                           thumbnail_attachment: :blob,
                           file_attachment: :blob,
-                          tag: :tag_name)
+                          tag: :tag_names)
     q = q.where(tag_id: nil) if filters[:tag_state] == 'untagged'
     q = q.where.not(tag_id: nil) if filters[:tag_state] == 'tagged'
     q = apply_material_tag_filter(q, filters, tag_graph)
@@ -42,7 +44,10 @@ class MaterialsController < ApplicationController
         .offset(offset)
         .to_a
 
-    response = { materials: MaterialRepr.list_many(materials, host: request.base_url),
+    response = { materials: MaterialRepr.list_many(
+                   materials,
+                   host: request.base_url,
+                   language_code: locale.language_code),
                  count: }
     if filters[:tag_id]
       response[:tag_scope] = material_index_tag_scope(filters, tag_graph)
@@ -55,6 +60,8 @@ class MaterialsController < ApplicationController
   end
 
   def show
+    locale = resolve_locale!
+
     material =
         Material
         .includes(:tag, :material_export_items)
@@ -63,15 +70,17 @@ class MaterialsController < ApplicationController
         .find_by(id: params[:id])
     return head :not_found unless material
 
-    wiki_page_body = material.tag&.tag_name&.wiki_page&.current_revision&.body
+    wiki_page_body = material.tag&.tag_name('ja')&.wiki_page&.current_revision&.body
 
-    render json: MaterialRepr.base(material, host: request.base_url).merge(wiki_page_body:)
+    render json: MaterialRepr.base(material, host: request.base_url,
+                                   language_code: locale.language_code).merge(wiki_page_body:)
   end
 
   def create
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
     tag_name_raw = params[:tag].to_s.strip
     file = params[:file]
     file_sha256 = MaterialFileSha256.from_upload(file)
@@ -89,13 +98,14 @@ class MaterialsController < ApplicationController
 
     begin
       Material.transaction do
-        tag = resolve_material_tag!(tag_name_raw)
+        tag = resolve_material_tag!(locale, tag_name_raw)
         material = Material.new(tag:, url:,
                                 created_by_user: current_user,
                                 updated_by_user: current_user)
         material.file.attach(uploaded_blob) if uploaded_blob
         material.save!
-        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user)
+        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user,
+                                           language_code: locale.language_code)
         upsert_export_paths!(material)
         MaterialVersionRecorder.record!(material:, event_type: :create,
                                         created_by_user: current_user)
@@ -107,7 +117,8 @@ class MaterialsController < ApplicationController
 
     if material
       log_thumbnail_generation(material, MaterialThumbnailGenerator.generate!(material))
-      render json: MaterialRepr.base(material, host: request.base_url), status: :created
+      render json: MaterialRepr.base(material, host: request.base_url,
+                                     language_code: locale.language_code), status: :created
     else
       render_validation_error material
     end
@@ -132,12 +143,14 @@ class MaterialsController < ApplicationController
     block = MaterialImportBlockMatcher.match_for_sha256(file_sha256)
     return render_material_import_block(block) if block
 
+    locale = resolve_locale!
+
     uploaded_blob = build_uploaded_material_blob!(file, file_sha256)
 
     begin
       Material.transaction do
         MaterialVersionRecorder.ensure_snapshot!(material, created_by_user: current_user)
-        tag = resolve_material_tag!(tag_name_raw)
+        tag = resolve_material_tag!(locale, tag_name_raw)
         material.assign_attributes(tag:, url:, updated_by_user: current_user)
         if uploaded_blob
           material.file.attach(uploaded_blob)
@@ -145,7 +158,8 @@ class MaterialsController < ApplicationController
           material.file.detach
         end
         material.save!
-        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user)
+        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user,
+                                           language_code: locale.language_code)
         upsert_export_paths!(material)
         MaterialVersionRecorder.record!(material:, event_type: :update,
                                         created_by_user: current_user)
@@ -157,7 +171,8 @@ class MaterialsController < ApplicationController
 
     log_thumbnail_generation(material, MaterialThumbnailGenerator.generate!(material))
 
-    render json: MaterialRepr.base(material, host: request.base_url)
+    render json: MaterialRepr.base(material, host: request.base_url,
+                                   language_code: locale.language_code)
   end
 
   def destroy
@@ -236,10 +251,8 @@ class MaterialsController < ApplicationController
     nil
   end
 
-  def resolve_material_tag! tag_name_raw
-    tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
-    tag = tag_name.tag
-    tag || Tag.create!(tag_name:, category: :material)
+  def resolve_material_tag! locale, tag_name_raw
+    Tag.find_or_create_by_tag_name!(locale, tag_name_raw, category: :material)
   end
 
   def material_index_needs_tag_name? filters
@@ -253,7 +266,12 @@ class MaterialsController < ApplicationController
   end
 
   def material_index_join_tag_name q
-    q.left_joins(tag: :tag_name)
+    q.left_joins(:tag).joins(<<~SQL.squish)
+      LEFT JOIN tag_names
+        ON tag_names.tag_id = tags.id
+       AND tag_names.language_code = 'ja'
+       AND tag_names.primary_flg = TRUE
+    SQL
   end
 
   def material_index_join_file_blob q
@@ -269,9 +287,11 @@ class MaterialsController < ApplicationController
 
   def apply_material_query q, term
     like = "%#{ ActiveRecord::Base.sanitize_sql_like(term) }%"
-    q.where('tag_names.name LIKE :q OR materials.url LIKE :q OR ' \
-            'material_file_blobs.filename LIKE :q',
-            q: like)
+    q.where(<<~SQL.squish, q: like)
+      tag_names.name LIKE :q
+      OR materials.url LIKE :q
+      OR material_file_blobs.filename LIKE :q
+    SQL
   end
 
   def apply_material_media_kind q, media_kind
@@ -323,8 +343,9 @@ class MaterialsController < ApplicationController
         end
     tags_by_id =
         Tag
-        .joins(:tag_name)
-        .where(id: scope_tag_ids)
+        .joins(:tag_names)
+        .where(id: scope_tag_ids,
+               tag_names: { language_code: 'ja', primary_flg: true })
         .pluck('tags.id', 'tag_names.name', 'tags.category', 'tags.deprecated_at')
         .each_with_object({ }) do |(id, name, category, deprecated_at), hash|
           hash[id] = { id:, name:, category:, deprecated: deprecated_at.present? }

backend/app/controllers/nico_tags_controller.rb

@@ -1,5 +1,7 @@
 class NicoTagsController < ApplicationController
   def index
+    locale = resolve_locale!
+
     name = params[:name].presence
     linked_tag = params[:linked_tag].presence
     link_status = params[:link_status].presence
@@ -15,30 +17,36 @@ class NicoTagsController < ApplicationController
     limit = 1 if limit < 1
 
     post_tag_max_sql =
-        PostTag
-        .select('tag_id, MAX(created_at) AS max_created_at')
-        .group('tag_id')
+        PostExternalTag
+        .select('external_tag_id, MAX(created_at) AS max_created_at')
+        .group('external_tag_id')
         .to_sql
 
-    q = Tag.nico_tags
-           .joins(:tag_name)
-           .joins("LEFT JOIN (#{ post_tag_max_sql }) post_tag_max " \
-                  'ON post_tag_max.tag_id = tags.id')
-           .includes(:tag_name, tag_name: :wiki_page, linked_tags: { tag_name: :wiki_page })
-    q = q.where('tag_names.name LIKE ?', "%#{ name }%") if name
+    q =
+        ExternalTag
+        .joins("LEFT JOIN (#{ post_tag_max_sql }) post_tag_max " \
+               'ON post_tag_max.external_tag_id = external_tags.id')
+        .includes(linked_tags: { tag_names: :wiki_page })
+    if name
+      q = q.where(('external_tags.name LIKE ? ' +
+                   "OR CONCAT(external_tags.platform, ':', external_tags.name) LIKE ?"),
+                  "%#{ name }%", "%#{ name }")
+    end
+
     if linked_tag
       linked_tag_ids =
-        Tag
-        .joins(:tag_name)
-        .where('tag_names.name LIKE ?', "%#{ linked_tag }%")
-        .pluck(:id)
+          Tag
+          .joins(:tag_names)
+          .where(tag_names: { language_code: 'ja', primary_flg: true })
+          .where('tag_names.name LIKE ?', "%#{ linked_tag }%")
+          .pluck(:id)
       linked_nico_tag_ids = NicoTagRelation.where(tag_id: linked_tag_ids).pluck(:nico_tag_id)
       q = q.where(id: linked_nico_tag_ids)
     end
     if link_status.in?(['linked', 'unlinked'])
       exists_sql =
           'EXISTS (SELECT 1 FROM nico_tag_relations ' \
-          'WHERE nico_tag_relations.nico_tag_id = tags.id)'
+          'WHERE nico_tag_relations.nico_tag_id = external_tags.id)'
       q = link_status == 'linked' ? q.where(exists_sql) : q.where("NOT #{ exists_sql }")
     end
 
@@ -46,54 +54,68 @@ class NicoTagsController < ApplicationController
     sort_sql =
         case order[0]
         when 'name'
-          'tag_names.name'
+          'external_tags.name'
         when 'updated_at'
           'post_tag_max.max_created_at'
         else
-          "tags.#{ order[0] }"
+          "external_tags.#{ order[0] }"
         end
-    tags = q.reselect('tags.*',
+    tags = q.reselect('external_tags.*',
                       Arel.sql('post_tag_max.max_created_at AS recent_post_tag_created_at'))
-            .order(Arel.sql("#{ sort_sql } #{ order[1] }, tags.id #{ order[1] }"))
+            .order(Arel.sql("#{ sort_sql } #{ order[1] }, external_tags.id #{ order[1] }"))
             .limit(limit)
             .offset((page - 1) * limit)
             .to_a
 
     render json: { tags: tags.map { |tag|
-      TagRepr.base(tag).merge(
+      external_tag_json(tag).merge(
           recent_post_tag_created_at: tag.recent_post_tag_created_at,
-          linked_tags: tag.linked_tags.map { |lt| TagRepr.base(lt) })
+          linked_tags: tag.linked_tags.map { |lt|
+            TagRepr.base(lt, language_code: locale.language_code)
+          })
     }, count: }
   end
 
+  def show
+    tag = ExternalTag.find(params[:id])
+
+    render json: external_tag_json(tag)
+  end
+
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
+
     id = params[:id].to_i
 
-    tag = Tag.find(id)
-    return render_bad_request('ニコニコ・タグを指定してください．') unless tag.nico?
+    tag = ExternalTag.find(id)
 
     linked_tag_names = params[:tags].to_s.split
     linked_tags = nil
 
     ApplicationRecord.transaction do
-      linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
-                                                          with_no_deerjikist: false)
-      if linked_tags.any? { |t| t.nico? }
-        raise Tag::NicoTagNormalisationError
-      end
+      linked_tags = Tag.normalise_tags!(locale, linked_tag_names,
+                                        with_tagme: false,
+                                        with_no_deerjikist: false)
 
-      TagVersioning.record_tag_snapshots!(linked_tags, created_by_user: current_user)
+      TagVersioning.record_tag_snapshots!(
+          linked_tags,
+          created_by_user: current_user,
+          language_code: locale.language_code)
 
       tag.linked_tags = linked_tags
       tag.save!
 
-      NicoTagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
+      NicoTagVersionRecorder.record!(external_tag: tag,
+                                     event_type: :update,
+                                     created_by_user: current_user)
     end
 
-    render json: tag.linked_tags.map { |t| TagRepr.base(t) }, status: :ok
+    render json: tag.linked_tags.map { |t|
+      TagRepr.base(t, language_code: locale.language_code)
+    }, status: :ok
   rescue Tag::NicoTagNormalisationError
     render_validation_error fields: { tags: ['ニコニコ・タグ同士は連携できません．'] }
   rescue ActiveRecord::RecordInvalid => e
@@ -102,6 +124,21 @@ class NicoTagsController < ApplicationController
 
   private
 
+  def external_tag_json tag
+    { id: tag.id,
+      name: "#{ tag.platform }:#{ tag.name }",
+      category: 'nico',
+      post_count: tag.post_count,
+      created_at: tag.created_at,
+      updated_at: tag.created_at,
+      deprecated_at: nil,
+      aliases: [],
+      parents: [],
+      has_wiki: false,
+      material_id: nil,
+      has_deerjikists: false }
+  end
+
   def render_nico_tag_form_record_invalid record
     if record.is_a?(TagName) || record.is_a?(Tag)
       render_validation_error fields: { tags: record.errors.full_messages.map { |message|

backend/app/controllers/post_versions_controller.rb

@@ -1,7 +1,10 @@
 class PostVersionsController < ApplicationController
   def index
     post_id = params[:post].presence
-    tag_id = params[:tag].presence
+    tag_id = params[:tag].presence&.to_i
+    external_tag_id = params[:external_tag].presence&.to_i
+    return head :bad_request if tag_id && external_tag_id
+
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
 
@@ -10,12 +13,6 @@ class PostVersionsController < ApplicationController
 
     offset = (page - 1) * limit
 
-    tag_name =
-        if tag_id
-          TagName.joins(:tag).find_by(tag: { id: tag_id })
-        end
-    return render json: { versions: [], count: 0 } if tag_id && tag_name.blank?
-
     q = PostVersion.joins(<<~SQL.squish)
           LEFT JOIN
             post_versions prev
@@ -23,17 +20,23 @@ class PostVersionsController < ApplicationController
               prev.post_id = post_versions.post_id
               AND prev.version_no = post_versions.version_no - 1
         SQL
-        .select('post_versions.*', 'prev.title AS prev_title', 'prev.url AS prev_url',
-                'prev.thumbnail_base AS prev_thumbnail_base', 'prev.tags AS prev_tags',
+        .select('post_versions.*',
+                'prev.title AS prev_title',
+                'prev.url AS prev_url',
+                'prev.thumbnail_base AS prev_thumbnail_base',
+                'prev.tags_json AS prev_tags_json',
                 'prev.video_ms AS prev_video_ms',
                 'prev.original_created_from AS prev_original_created_from',
                 'prev.original_created_before AS prev_original_created_before')
     q = q.where('post_versions.post_id = ?', post_id) if post_id
-    if tag_name
-      escaped = ActiveRecord::Base.sanitize_sql_like(tag_name.name)
-      q = q.where(("CONCAT(' ', post_versions.tags, ' ') LIKE :kw " +
-                   "OR CONCAT(' ', prev.tags, ' ') LIKE :kw"),
-                  kw: "% #{ escaped } %")
+    if external_tag_id || (tag_id && !(Tag.exists?(id: tag_id)))
+      q = q.where('JSON_CONTAINS(post_versions.tags_json,' +
+                  "JSON_OBJECT('external_tag_id', #{ external_tag_id || tag_id })) " +
+                  'OR JSON_CONTAINS(prev.tags_json,' +
+                  "JSON_OBJECT('external_tag_id', #{ external_tag_id || tag_id }))")
+    elsif tag_id
+      q = q.where("JSON_CONTAINS(post_versions.tags_json, JSON_OBJECT('tag_id', #{ tag_id })) " +
+                  "OR JSON_CONTAINS(prev.tags_json, JSON_OBJECT('tag_id', #{ tag_id }))")
     end
 
     count = q.except(:select, :order, :limit, :offset).count
@@ -48,77 +51,91 @@ class PostVersionsController < ApplicationController
   private
 
   def serialise_versions rows
+    rows = rows.to_a
     user_ids = rows.map(&:created_by_user_id).compact.uniq
     users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
+    snapshots = rows.flat_map { |row|
+      [normalise_json(row.tags_json),
+       normalise_json(row.attributes['prev_tags_json']) || []]
+    }
+    external_tag_names = external_tag_names_for(snapshots)
 
     rows.map do |row|
-      cur_tags = split_tags(row.tags)
-      prev_tags = split_tags(row.attributes['prev_tags'])
+      cur_tags = snapshot_tag_literals(normalise_json(row.tags_json), external_tag_names)
+      prev_tags = snapshot_tag_literals(
+          normalise_json(row.attributes['prev_tags_json']) || [], external_tag_names)
 
-      {
-        post_id: row.post_id,
+      { post_id: row.post_id,
         version_no: row.version_no,
         event_type: row.event_type,
-        title: {
-          current: row.title,
-          prev: row.attributes['prev_title']
-        },
-        url: {
-          current: row.url,
-          prev: row.attributes['prev_url']
-        },
-        thumbnail: {
-          current: nil,
-          prev: nil
-        },
-        thumbnail_base: {
-          current: row.thumbnail_base,
-          prev: row.attributes['prev_thumbnail_base']
-        },
-        video_ms: {
-          current: row.video_ms,
-          prev: row.attributes['prev_video_ms']
-        },
+        title: { current: row.title, prev: row.attributes['prev_title'] },
+        url: { current: row.url, prev: row.attributes['prev_url'] },
+        thumbnail: { current: nil, prev: nil },
+        thumbnail_base: { current: row.thumbnail_base,
+                          prev: row.attributes['prev_thumbnail_base'] },
+        video_ms: { current: row.video_ms, prev: row.attributes['prev_video_ms'] },
         tags: build_version_tags(cur_tags, prev_tags),
         original_created_from: {
-          current: row.original_created_from&.iso8601,
-          prev: row.attributes['prev_original_created_from']&.iso8601
-        },
+            current: row.original_created_from&.iso8601,
+            prev: row.attributes['prev_original_created_from']&.iso8601 },
         original_created_before: {
-          current: row.original_created_before&.iso8601,
-          prev: row.attributes['prev_original_created_before']&.iso8601
-        },
+            current: row.original_created_before&.iso8601,
+            prev: row.attributes['prev_original_created_before']&.iso8601 },
         created_at: row.created_at.iso8601,
         created_by_user:
-          if row.created_by_user_id
-            {
-              id: row.created_by_user_id,
-              name: users_by_id[row.created_by_user_id]
-            }
-          end
-      }
+            if row.created_by_user_id
+              { id: row.created_by_user_id,
+                name: users_by_id[row.created_by_user_id] }
+            end }
     end
   end
 
-  def build_version_tags(cur_tags, prev_tags)
+  def external_tag_names_for snapshots
+    ids = snapshots.flatten.filter_map { _1['external_tag_id'] }.uniq
+    names = ExternalTag.where(id: ids).pluck(:id, :platform, :name).to_h { |id, platform, name|
+      [id, "#{ platform }:#{ name }"]
+    }
+    missing_ids = ids - names.keys
+
+    NicoTagVersion
+        .where(tag_id: missing_ids)
+        .order(:tag_id, version_no: :desc)
+        .pluck(:tag_id, :name)
+        .each { |id, name| names[id] ||= name }
+
+    names
+  end
+
+  def snapshot_tag_literals snapshots, external_tag_names
+    snapshots
+        .filter_map { |snapshot|
+          if snapshot.key?('tag_id')
+            [tag_category_order(snapshot['category']),
+             Post.tag_snapshot_literal(snapshot)]
+          elsif external_tag_names[snapshot['external_tag_id']]
+            [6, external_tag_names[snapshot['external_tag_id']]]
+          end
+        }
+        .sort_by { |order, name| [order, name.downcase] }
+        .map(&:second)
+  end
+
+  def tag_category_order category
+    ['deerjikist', 'meme', 'character', 'general', 'material', 'meta'].index(category) || 6
+  end
+
+  def build_version_tags cur_tags, prev_tags
     (cur_tags | prev_tags).map do |name|
       type =
-        if cur_tags.include?(name) && prev_tags.include?(name)
-          'context'
-        elsif cur_tags.include?(name)
-          'added'
-        else
-          'removed'
-        end
+          if cur_tags.include?(name) && prev_tags.include?(name)
+            'context'
+          elsif cur_tags.include?(name)
+            'added'
+          else
+            'removed'
+          end
 
-      {
-        name:,
-        type:
-      }
+      { name:, type: }
     end
   end
-
-  def split_tags(tags)
-    tags.to_s.split(/\s+/).reject(&:blank?)
-  end
 end

backend/app/controllers/posts_controller.rb

@@ -7,6 +7,8 @@ class PostsController < ApplicationController
   end
 
   def index
+    locale = resolve_locale!
+
     url = params[:url].presence
     title = params[:title].presence
     original_created_from = params[:original_created_from].presence
@@ -36,8 +38,8 @@ class PostsController < ApplicationController
     offset = (page - 1) * limit
 
     pt_max_sql =
-        PostTag
-        .select('post_id, MAX(updated_at) AS max_updated_at')
+        PostVersion
+        .select('post_id, MAX(created_at) AS max_updated_at')
         .group('post_id')
         .to_sql
 
@@ -46,13 +48,12 @@ class PostsController < ApplicationController
         'COALESCE(pt_max.max_updated_at, posts.updated_at))'
 
     q =
-        filtered_posts
+        filtered_posts(locale)
         .joins("LEFT JOIN (#{ pt_max_sql }) pt_max ON pt_max.post_id = posts.id")
         .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
-        .preload(:uploaded_user, :parents, :children,
-                 active_post_tags: [:sections,
-                                    { tag: [:deerjikists, :materials,
-                                            { tag_name: :wiki_page }] }])
+        .preload(:external_tags, :uploaded_user, :parents, :children,
+                 post_tags: [:sections, { tag: [:deerjikists, :materials,
+                                                { tag_names: :wiki_page }] }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -91,7 +92,8 @@ class PostsController < ApplicationController
     q = q.except(:select, :order)
 
     render json: { posts: posts.map { |post|
-      PostRepr.base(post).merge(updated_at: post.updated_at_all).tap do |json|
+      PostRepr.base(post, language_code: locale.language_code)
+              .merge(updated_at: post.updated_at_all).tap do |json|
         json['thumbnail'] =
             if post.thumbnail.attached?
               rails_storage_proxy_url(post.thumbnail, only_path: false)
@@ -103,16 +105,19 @@ class PostsController < ApplicationController
   end
 
   def random
-    post = filtered_posts.preload(:uploaded_user, :parents, :children,
-                                  active_post_tags: [:sections,
-                                                     { tag: [:deerjikists, :materials,
-                                                             { tag_name: :wiki_page }] }])
-                         .with_attached_thumbnail
-                         .order('RAND()')
-                         .first
+    locale = resolve_locale!
+
+    post =
+        filtered_posts(locale)
+        .preload(:uploaded_user, :parents, :children,
+                 post_tags: [:sections, { tag: [:deerjikists, :materials,
+                                                { tag_names: :wiki_page }] }])
+        .with_attached_thumbnail
+        .order('RAND()')
+        .first
     return head :not_found unless post
 
-    render json: PostRepr.base(post, current_user)
+    render json: PostRepr.base(post, current_user, language_code: locale.language_code)
   end
 
   def metadata
@@ -187,12 +192,13 @@ class PostsController < ApplicationController
   end
 
   def show
+    locale = resolve_locale!
+
     post =
         Post
         .includes(:uploaded_user, :parents, :children,
-                  active_post_tags: [:sections,
-                                     { tag: [:deerjikists, :materials,
-                                             { tag_name: :wiki_page }] }])
+                  post_tags: [:sections, { tag: [:deerjikists, :materials,
+                                                 { tag_names: :wiki_page }] }])
         .with_attached_thumbnail
         .find_by(id: params[:id])
     return head :not_found unless post
@@ -206,18 +212,21 @@ class PostsController < ApplicationController
                                  parent_posts:,
                                  child_posts:,
                                  sibling_posts:,
-                                 related:)
-                         .merge(tags: build_tag_tree_for(post))
+                                 related:,
+                                 language_code: locale.language_code)
+                         .merge(tags: build_tag_tree_for(post, locale.language_code))
   end
 
   def create
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
+
     preflight = PostCreatePreflight.new(
         attributes: post_create_attributes,
         thumbnail: params[:thumbnail],
-        host: request.base_url).run
+        host: request.base_url).run(locale)
     return render json: dry_run_json(preflight) if bool?(:dry)
     if preflight[:existing_post_id].present?
       post = Post.new(url: preflight[:url])
@@ -243,10 +252,10 @@ class PostsController < ApplicationController
                                    :post_tag_specs,
                                    :tag_sections,
                                    :normalised_parent_post_ids).symbolize_keys).merge(
-                               thumbnail: params[:thumbnail])).create!
+                               thumbnail: params[:thumbnail])).create!(locale)
 
     post.reload
-    render json: PostRepr.base(post), status: :created
+    render json: PostRepr.base(post, language_code: locale.language_code), status: :created
   rescue PostCreatePreflight::ValidationFailed => e
     render_validation_error fields: e.fields, base: e.base_errors
   rescue Tag::NicoTagNormalisationError
@@ -272,13 +281,18 @@ class PostsController < ApplicationController
     return head :forbidden unless current_user.gte_member?
     return head :unsupported_media_type unless request.content_mime_type == Mime[:multipart_form]
     return head :payload_too_large if request.content_length.to_i > MAX_BULK_REQUEST_BYTES
+
+    locale = resolve_locale!
+
     posts = parse_bulk_posts_manifest
     thumbnails = parse_bulk_thumbnails(posts.length)
+
     result = PostBulkCreator.new(
         actor: current_user,
         posts:,
         thumbnails:,
-        host: request.base_url).run
+        host: request.base_url).run(locale)
+
     render json: result
   rescue JSON::ParserError
     render_bad_request 'posts manifest の JSON が不正です．'
@@ -311,6 +325,7 @@ class PostsController < ApplicationController
     base_version_no = parse_base_version_no
     return render_bad_request('base_version_no は必須です．') if !(force) && !(base_version_no)
 
+    locale = Locale.find_by(code: params[:locale].presence) || Locale.nipponese
     title = params[:title].presence
     tag_names = params[:tags].to_s.split
     original_created_from = params[:original_created_from]
@@ -330,9 +345,10 @@ class PostsController < ApplicationController
         base_version = post.post_versions.find_by!(version_no: base_version_no)
 
         base_snapshot = post_snapshot_from_version(base_version)
-        current_snapshot = post_snapshot_from_record(post)
+        current_snapshot = post_snapshot_from_record(post, locale)
       end
-      incoming_snapshot = post_incoming_snapshot(title:,
+      incoming_snapshot = post_incoming_snapshot(locale:,
+                                                 title:,
                                                  original_created_from:,
                                                  original_created_before:,
                                                  tag_names:,
@@ -361,14 +377,14 @@ class PostsController < ApplicationController
             end
           end
 
-      apply_post_snapshot!(post, snapshot_to_apply)
+      apply_post_snapshot!(locale, post, snapshot_to_apply)
     end
 
     return render json: conflict_json, status: :conflict if conflict_json
 
     post.reload
-    json = PostRepr.base(post, current_user)
-    json['tags'] = build_tag_tree_for(post)
+    json = PostRepr.base(post, current_user, language_code: locale.language_code)
+    json['tags'] = build_tag_tree_for(post, locale.language_code)
     render json:, status: :ok
   rescue Tag::NicoTagNormalisationError
     render_validation_error fields: { tags: ['ニコニコ・タグは直接指定できません．'] }
@@ -384,65 +400,21 @@ class PostsController < ApplicationController
     render_post_form_record_invalid e.record
   end
 
-  def changes
-    id = params[:id].presence
-    tag_id = params[:tag].presence
-    page = (params[:page].presence || 1).to_i
-    limit = (params[:limit].presence || 20).to_i
-
-    page = 1 if page < 1
-    limit = 1 if limit < 1
-
-    offset = (page - 1) * limit
-
-    pts = PostTag.with_discarded
-    pts = pts.where(post_id: id) if id.present?
-    pts = pts.where(tag_id:) if tag_id.present?
-    pts = pts.includes(:post, :created_user, :deleted_user,
-                       tag: [:deerjikists, :materials, { tag_name: :wiki_page }])
-
-    events = []
-    pts.each do |pt|
-      tag = TagRepr.base(pt.tag)
-      post = pt.post
-
-      events << Event.new(
-          post:,
-          tag:,
-          user: pt.created_user && { id: pt.created_user.id, name: pt.created_user.name },
-          change_type: 'add',
-          timestamp: pt.created_at)
-
-      if pt.discarded_at
-        events << Event.new(
-            post:,
-            tag:,
-            user: pt.deleted_user && { id: pt.deleted_user.id, name: pt.deleted_user.name },
-            change_type: 'remove',
-            timestamp: pt.discarded_at)
-      end
-    end
-    events.sort_by!(&:timestamp)
-    events.reverse!
-
-    render json: { changes: (events.slice(offset, limit) || []).as_json, count: events.size }
-  end
-
   private
 
-  def filtered_posts
+  def filtered_posts locale
     tag_names = params[:tags].to_s.split
     match_type = params[:match]
     if tag_names.present?
-      filter_posts_by_tags(tag_names, match_type)
+      filter_posts_by_tags(locale, tag_names, match_type)
     else
       Post.all
     end
   end
 
-  def filter_posts_by_tags tag_names, match_type
+  def filter_posts_by_tags locale, tag_names, match_type
     literals = tag_names.map do |raw_name|
-      { name: TagName.canonicalise(raw_name.sub(/\Anot:/i, '')).first,
+      { name: TagName.canonicalise(locale, raw_name.sub(/\Anot:/i, '')).first,
         negative: raw_name.downcase.start_with?('not:') }
     end
 
@@ -450,11 +422,11 @@ class PostsController < ApplicationController
 
     if match_type == 'any'
       literals.reduce(Post.none) do |posts, literal|
-        posts.or(tag_literal_relation(literal[:name], negative: literal[:negative]))
+        posts.or(tag_literal_relation(locale, literal[:name], negative: literal[:negative]))
       end
     else
       literals.reduce(Post.all) do |posts, literal|
-        ids = tagged_post_ids_for(literal[:name])
+        ids = tagged_post_ids_for(locale, literal[:name])
         if literal[:negative]
           posts.where.not(id: ids)
         else
@@ -464,8 +436,8 @@ class PostsController < ApplicationController
     end
   end
 
-  def tag_literal_relation name, negative:
-    ids = tagged_post_ids_for(name)
+  def tag_literal_relation locale, name, negative:
+    ids = tagged_post_ids_for(locale, name)
     if negative
       Post.where.not(id: ids)
     else
@@ -473,8 +445,20 @@ class PostsController < ApplicationController
     end
   end
 
-  def tagged_post_ids_for(name) =
-      Post.joins(tags: :tag_name).where(tag_names: { name: }).select(:id)
+  def tagged_post_ids_for locale, name
+    posts_by_internal_tags =
+        Post
+        .joins(tags: :tag_names)
+        .where(tag_names: { language_code: locale.language_code, name: })
+        .select(:id)
+
+    posts_by_external_tags =
+        Post
+        .joins(:external_tags)
+        .where("CONCAT(external_tags.platform, ':', external_tags.name) = ?", name)
+
+    (posts_by_internal_tags + posts_by_external_tags).uniq(&:id)
+  end
 
   def sync_post_tags! post, desired_tags, sections
     desired_tags.each do |t|
@@ -502,13 +486,13 @@ class PostsController < ApplicationController
       end
     end
 
-    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
-      pt.discard_by!(current_user)
+    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each do |pt|
+      pt.destroy!
     end
   end
 
-  def build_tag_tree_for post
-    post_tags = post.active_post_tags.reject { |post_tag| post_tag.tag.deprecated? }
+  def build_tag_tree_for post, language_code = 'ja'
+    post_tags = post.post_tags.reject { |post_tag| post_tag.tag.deprecated? }
     tags = post_tags.map(&:tag)
     tag_ids = tags.map(&:id)
 
@@ -537,7 +521,7 @@ class PostsController < ApplicationController
       sections = sections_by_tag_id.fetch(tag_id, [])
 
       if path.include?(tag_id)
-        return TagRepr.inline(tag).merge(children: [], sections:)
+        return TagRepr.inline(tag, language_code:).merge(children: [], sections:)
       end
 
       if memo.key?(tag_id)
@@ -549,10 +533,13 @@ class PostsController < ApplicationController
 
       children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
 
-      memo[tag_id] = TagRepr.inline(tag).merge(children:, sections:)
+      memo[tag_id] = TagRepr.inline(tag, language_code:).merge(children:, sections:)
     end
 
-    root_ids.filter_map { |id| build_node.call(id, []) }
+    internal_tags = root_ids.filter_map { |id| build_node.call(id, []) }
+    external_tags =
+        post.external_tags.map { ExternalTagRepr.inline(_1).merge(children: [], sections: []) }
+    internal_tags + external_tags
   end
 
   def sibling_posts_by_parent parent_post_ids
@@ -699,43 +686,49 @@ class PostsController < ApplicationController
   end
 
   def editable_tag_names_from_version version
-    version.tags.to_s.split.reject { |name| name.downcase.start_with?('nico:') }.sort
+    version.tags_json
+        .select { _1.key?('tag_id') }
+        .map { Post.tag_snapshot_literal(_1) }
+        .compact
+        .sort
   end
 
-  def post_snapshot_from_record post
+  def post_snapshot_from_record post, locale
     { title: post.title,
       video_ms: post.video_ms,
       original_created_from: snapshot_time(post.original_created_from),
       original_created_before: snapshot_time(post.original_created_before),
-      tag_names: editable_tag_names_from_post(post),
+      tag_names: editable_tag_names_from_post(post, locale.language_code),
       parent_post_ids: post.parent_posts.order(:id).pluck(:id) }
   end
 
-  def editable_tag_names_from_post post
+  def editable_tag_names_from_post post, language_code
     post
         .post_tags
-        .kept
-        .joins(tag: :tag_name)
-        .merge(Tag.not_nico)
+        .joins(tag: :tag_names)
         .merge(Tag.where(deprecated_at: nil))
-        .includes(:sections, tag: :tag_name)
+        .where(tag_names: { language_code:, primary_flg: true })
+        .includes(:sections, tag: :tag_names)
         .order('tag_names.name')
         .map do |post_tag|
-      name = post_tag.tag.tag_name.name
+      name = post_tag.tag.name(language_code)
       sections = post_tag.sections.sort_by(&:begin_ms)
 
       next name if sections.empty?
 
       "#{ name }#{ sections.map { Post.section_literal(_1) }.join }"
-    end
+    end.compact.sort
   end
 
-  def post_incoming_snapshot title:, original_created_from:, original_created_before:,
+  def post_incoming_snapshot locale:, title:, original_created_from:, original_created_before:,
                              tag_names:, video_ms_param:, duration_param:, parent_post_ids:
     validate_original_created_values!(original_created_from, original_created_before)
-    Tag.normalise_tags!(tag_names, with_tagme: false, deny_deprecated: true,
-                                        with_sections: true) =>
-        { tags:, sections: }
+
+    Tag.normalise_tags!(locale, tag_names,
+                        with_tagme: false,
+                        with_no_deerjikist: false,
+                        deny_deprecated: true,
+                        with_sections: true) => { tags:, sections: }
 
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
     video_ms = normalise_video_ms(tags, video_ms_param:, duration_param:)
@@ -746,7 +739,7 @@ class PostsController < ApplicationController
       original_created_from: snapshot_time(original_created_from),
       original_created_before: snapshot_time(original_created_before),
       tag_names: tags.uniq(&:id).map { |tag|
-        "#{ tag.name }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
+        "#{ tag.name(locale.language_code) }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
       }.sort,
       parent_post_ids: parent_post_ids.sort }
   end
@@ -870,7 +863,7 @@ class PostsController < ApplicationController
     (added_by_current & removed_by_me).present? || (removed_by_current & added_by_me).present?
   end
 
-  def apply_post_snapshot! post, snapshot
+  def apply_post_snapshot! locale, post, snapshot
     PostVersionRecorder.ensure_snapshot!(post, created_by_user: current_user)
 
     post.update!(title: snapshot[:title],
@@ -878,15 +871,13 @@ class PostsController < ApplicationController
                  original_created_from: snapshot[:original_created_from],
                  original_created_before: snapshot[:original_created_before])
 
-    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false,
-                                               deny_deprecated: true,
-                                               with_sections: true) =>
-        { tags: editable_tags, sections: }
-    TagVersioning.record_tag_snapshots!(editable_tags, created_by_user: current_user)
+    Tag.normalise_tags!(locale, snapshot[:tag_names],
+                        with_tagme: false,
+                        deny_deprecated: true,
+                        with_sections: true) => { tags:, sections: }
+    TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user,
+                                        language_code: locale.language_code)
 
-    readonly_tags = post.tags.nico.to_a
-
-    tags = readonly_tags + editable_tags
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
 
     post.video_ms = tags.any? { _1.id == Tag.video.id } ? snapshot[:video_ms] : nil

backend/app/controllers/tag_children_controller.rb

@@ -10,7 +10,6 @@ class TagChildrenController < ApplicationController
 
     parent = Tag.find(parent_id)
     child = Tag.find(child_id)
-    return render_bad_request('ニコニコ・タグの階層は変更できません．') if parent.nico? || child.nico?
 
     ApplicationRecord.transaction do
       TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
@@ -33,7 +32,6 @@ class TagChildrenController < ApplicationController
 
     parent = Tag.find(parent_id)
     child = Tag.find(child_id)
-    return render_bad_request('ニコニコ・タグの階層は変更できません．') if parent.nico? || child.nico?
 
     ApplicationRecord.transaction do
       TagVersioning.ensure_snapshot!(child, created_by_user: current_user)

backend/app/controllers/tag_versions_controller.rb

@@ -1,5 +1,6 @@
 class TagVersionsController < ApplicationController
   def index
+    locale = resolve_locale!
     tag_id = params[:id].presence
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
@@ -18,7 +19,8 @@ class TagVersionsController < ApplicationController
         SQL
       .select('tag_versions.*', 'prev.name AS prev_name', 'prev.category AS prev_category',
               'prev.deprecated_at AS prev_deprecated_at',
-              'prev.aliases AS prev_aliases', 'prev.parent_tag_ids AS prev_parent_tag_ids')
+              'prev.aliases AS prev_aliases', 'prev.names AS prev_names',
+              'prev.parent_tag_ids AS prev_parent_tag_ids')
     q = q.where('tag_versions.tag_id = ?', tag_id) if tag_id
 
     count = q.except(:select, :order, :limit, :offset).count
@@ -27,18 +29,20 @@ class TagVersionsController < ApplicationController
                 .limit(limit)
                 .offset(offset)
 
-    render json: { versions: serialise_versions(versions), count: }
+    render json: { versions: serialise_versions(versions, locale.language_code), count: }
   end
 
   private
 
-  def serialise_versions rows
+  def serialise_versions rows, language_code
     user_ids = rows.map(&:created_by_user_id).compact.uniq
     users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
 
     rows.map do |row|
-      cur_aliases = split_values(row.aliases)
-      prev_aliases = split_values(row.attributes['prev_aliases'])
+      current_names = names_for_locale(row.names, language_code)
+      previous_names = names_for_locale(row.attributes['prev_names'], language_code)
+      cur_aliases = current_names.fetch('aliases', []).map { _1.fetch('name') }
+      prev_aliases = previous_names.fetch('aliases', []).map { _1.fetch('name') }
 
       cur_parent_tag_ids = split_parent_tag_ids(row.parent_tag_ids)
       prev_parent_tag_ids = split_parent_tag_ids(row.attributes['prev_parent_tag_ids'])
@@ -47,21 +51,22 @@ class TagVersionsController < ApplicationController
 
       tags_by_id =
           Tag
-          .includes(:tag_name, :materials, { tag_name: :wiki_page })
+          .includes(:tag_names, :materials, tag_names: :wiki_page)
           .where(id: all_parent_tag_ids)
           .index_by(&:id)
 
       parent_tags =
           build_version_values(cur_parent_tag_ids, prev_parent_tag_ids, key: :tag_id)
           .map do |h|
-            { tag: TagRepr.base(tags_by_id[h[:tag_id]]),
+            { tag: TagRepr.base(tags_by_id[h[:tag_id]], language_code:),
               type: h[:type] }
           end
 
       { tag_id: row.tag_id,
         version_no: row.version_no,
         event_type: row.event_type,
-        name: { current: row.name, prev: row.attributes['prev_name'] },
+        names: row.names,
+        name: { current: current_names['name'], prev: previous_names['name'] },
         category: { current: row.category, prev: row.attributes['prev_category'] },
         deprecated_at: { current: row.deprecated_at&.iso8601,
                          prev: row.attributes['prev_deprecated_at']&.iso8601 },
@@ -91,5 +96,12 @@ class TagVersionsController < ApplicationController
 
   def split_values(values) = values.to_s.split(/\s+/).reject(&:blank?)
 
+  def names_for_locale names, language_code
+    values = names.is_a?(String) ? JSON.parse(names) : names
+    values&.fetch(language_code, {}) || {}
+  rescue JSON::ParserError
+    {}
+  end
+
   def split_parent_tag_ids(values) = split_values(values).map(&:to_i)
 end

backend/app/controllers/tags_controller.rb

@@ -5,6 +5,8 @@ require 'set'
 
 class TagsController < ApplicationController
   def index
+    locale = resolve_locale!
+
     post_id = params[:post]
 
     name = params[:name].presence
@@ -34,49 +36,161 @@ class TagsController < ApplicationController
 
     offset = (page - 1) * limit
 
-    q =
+    tags =
         if post_id.present?
-          Tag.joins(:posts, :tag_name)
+          Tag
+              .joins(:posts, :tag_names)
+              .where(tag_names: { language_code: locale.language_code, primary_flg: true },
+                     posts: { id: post_id })
         else
-          Tag.joins(:tag_name)
+          Tag
+              .joins(:tag_names)
+              .where(tag_names: { language_code: locale.language_code, primary_flg: true })
         end
-        .includes(:tag_name, :materials, tag_name: :wiki_page)
-    q = q.where(posts: { id: post_id }) if post_id.present?
 
-    q = q.where('tag_names.name LIKE ?', "%#{ name }%") if name
-    q = q.where(category:) if category
-    q = q.where('tags.post_count >= ?', post_count_between[0]) if post_count_between[0]
-    q = q.where('tags.post_count <= ?', post_count_between[1]) if post_count_between[1]
-    q = q.where('tags.created_at >= ?', created_between[0]) if created_between[0]
-    q = q.where('tags.created_at <= ?', created_between[1]) if created_between[1]
-    q = q.where('tags.updated_at >= ?', updated_between[0]) if updated_between[0]
-    q = q.where('tags.updated_at <= ?', updated_between[1]) if updated_between[1]
-    if deprecated_given
-      q = deprecated ? q.where.not(deprecated_at: nil) : q.where(deprecated_at: nil)
+    external_tags =
+        if post_id.present?
+          ExternalTag.joins(:posts).where(posts: { id: post_id })
+        else
+          ExternalTag.all
+        end
+
+    if name
+      tags = tags.where('tag_names.name LIKE ?', "%#{ name }%")
+      external_tags =
+          external_tags.where("CONCAT(external_tags.platform, ':', external_tags.name) LIKE ?",
+                              "%#{ name }%")
     end
 
+    if category == 'nico'
+      tags = tags.none
+    elsif category
+      tags = tags.where(category:)
+      external_tags = external_tags.none
+    end
+
+    if post_count_between[0]
+      tags = tags.where('tags.post_count >= ?', post_count_between[0])
+      external_tags = external_tags.where('external_tags.post_count >= ?', post_count_between[0])
+    end
+
+    if post_count_between[1]
+      tags = tags.where('tags.post_count <= ?', post_count_between[1])
+      external_tags = external_tags.where('external_tags.post_count <= ?', post_count_between[1])
+    end
+
+    if created_between[0]
+      tags = tags.where('tags.created_at >= ?', created_between[0])
+      external_tags = external_tags.where('external_tags.created_at >= ?', created_between[0])
+    end
+
+    if created_between[1]
+      tags = tags.where('tags.created_at <= ?', created_between[1])
+      external_tags = external_tags.where('external_tags.created_at <= ?', created_between[1])
+    end
+
+    if updated_between[0]
+      tags = tags.where('tags.updated_at >= ?', updated_between[0])
+      external_tags = external_tags.where('external_tags.created_at >= ?', updated_between[0])
+    end
+
+    if updated_between[1]
+      tags = tags.where('tags.updated_at <= ?', updated_between[1])
+      external_tags = external_tags.where('external_tags.created_at <= ?', updated_between[1])
+    end
+
+    if deprecated_given
+      if deprecated
+        tags = tags.where.not(deprecated_at: nil)
+        external_tags = external_tags.none
+      else
+        tags = tags.where(deprecated_at: nil)
+      end
+    end
+
+    tag_sql = tags.select("'tag' AS source",
+                          'tags.id',
+                          'tag_names.name',
+                          'tags.category',
+                          'tags.post_count',
+                          'tags.created_at',
+                          'tags.updated_at',
+                          'tags.deprecated_at').to_sql
+
+    external_tag_sql = external_tags.select(
+        "'external_tag' AS source",
+        'external_tags.id',
+        "CONCAT(external_tags.platform, ':', external_tags.name) AS name",
+        "'nico' AS category",
+        'external_tags.post_count',
+        'external_tags.created_at',
+        'external_tags.created_at AS updated_at',
+        'NULL AS deprecated_at').to_sql
+
+    union_sql = "#{ tag_sql } UNION ALL #{ external_tag_sql }"
+
     sort_sql =
-        case order[0]
-        when 'name'
-          'tag_names.name'
-        when 'category'
-          'CASE tags.category ' +
+        if order[0] == 'category'
+          'CASE category ' +
           "WHEN 'deerjikist' THEN 0 " +
           "WHEN 'meme' THEN 1 " +
           "WHEN 'character' THEN 2 " +
           "WHEN 'general' THEN 3 " +
           "WHEN 'material' THEN 4 " +
           "WHEN 'meta' THEN 5 " +
-          "WHEN 'nico' THEN 6 END"
+          "WHEN 'nico' THEN 6 " +
+          'END'
         else
-          "tags.#{ order[0] }"
+          order[0]
         end
-    tags = q.order(Arel.sql("#{ sort_sql } #{ order[1] }, tags.id #{ order[1] }"))
-            .limit(limit)
-            .offset(offset)
-            .to_a
 
-    render json: { tags: TagRepr.many(tags), count: q.size }
+    connection = ApplicationRecord.connection
+
+    count = connection.select_value(<<~SQL)
+      SELECT
+        COUNT(0)
+      FROM
+        (#{ union_sql }) legacy_tags
+    SQL
+
+    rows = connection.select_all(<<~SQL).to_a
+      SELECT
+        source
+      , id
+      FROM
+        (#{ union_sql }) legacy_tags
+      ORDER BY
+        #{ sort_sql } #{ order[1] }
+      , id #{ order[1] }
+      , source #{ order[1] }
+      LIMIT
+        #{ limit }
+      OFFSET
+        #{ offset }
+    SQL
+
+    tag_ids = rows.filter { _1['source'] == 'tag' }.map { _1['id'] }
+    external_tag_ids = rows.filter { _1['source'] == 'external_tag' }.map { _1['id'] }
+
+    tags_by_id =
+        Tag
+        .joins(:tag_names)
+        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .where(tag_names: { language_code: locale.language_code, primary_flg: true },
+               id: tag_ids)
+        .index_by(&:id)
+    external_tags_by_id =
+        ExternalTag
+        .where(id: external_tag_ids)
+        .index_by(&:id)
+
+    render json: { tags: rows.map { |row|
+      if row['source'] == 'tag'
+        TagRepr.base(tags_by_id.fetch(row['id']), language_code: locale.language_code)
+      else
+        external_tag_json(external_tags_by_id.fetch(row['id']))
+      end
+    }, count: }
   end
 
   def with_depth
@@ -84,7 +198,8 @@ class TagsController < ApplicationController
     parent_tag_id = nil if parent_tag_id <= 0
     material_filter = material_filter_param(default: 'any')
 
-    graph = build_with_depth_graph(material_filter)
+    locale = resolve_locale!
+    graph = build_with_depth_graph(material_filter, locale.language_code)
 
     tag_ids =
         if parent_tag_id
@@ -99,137 +214,223 @@ class TagsController < ApplicationController
   end
 
   def autocomplete
+    locale = resolve_locale!
+
     q = params[:q].to_s.strip.sub(/\Anot:/i, '')
+    prefix = "#{ ActiveRecord::Base.sanitize_sql_like(q) }%"
 
     with_nico = bool?(:nico, default: true)
     present_only = bool?(:present, default: true)
 
     alias_rows =
         TagName
-        .where('name LIKE ?', "#{ q }%")
-        .where.not(canonical_id: nil)
-        .pluck(:canonical_id, :name)
+        .where(language_code: locale.language_code, primary_flg: false)
+        .where('name LIKE ?', prefix)
+        .pluck(:tag_id, :name)
 
-    matched_alias_by_tag_name_id = { }
-    canonical_ids = []
-
-    alias_rows.each do |canonical_id, alias_name|
-      canonical_ids << canonical_id
-      matched_alias_by_tag_name_id[canonical_id] ||= alias_name
+    matched_alias_by_tag_id = { }
+    tag_ids = []
+    alias_rows.each do |tag_id, alias_name|
+      tag_ids << tag_id
+      matched_alias_by_tag_id[tag_id] ||= alias_name
     end
 
-    base = Tag.joins(:tag_name)
-              .includes(:tag_name, :materials, tag_name: :wiki_page)
-              .where(deprecated_at: nil)
+    base =
+        Tag
+        .joins(:tag_names)
+        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .where(tag_names: { language_code: locale.language_code, primary_flg: true },
+               deprecated_at: nil)
     base = base.where('tags.post_count > 0') if present_only
 
-    canonical_hit =
-        base
-        .where(((with_nico ? '(tags.category = ? AND tag_names.name LIKE ?) OR ' : '') +
-                'tag_names.name LIKE ?'),
-               *(with_nico ? ['nico', "nico:#{ q }%"] : []), "#{ q }%")
+    canonical_hit = base.where('tag_names.name LIKE ?', prefix)
 
-    tags =
-        if canonical_ids.present?
-          canonical_hit.or(base.where(tag_name_id: canonical_ids.uniq))
-        else
-          canonical_hit
-        end
+    internal_tags = canonical_hit.or(base.where(id: tag_ids.uniq))
 
-    tags = tags.order(Arel.sql('post_count DESC, tag_names.name')).limit(20).to_a
+    internal_rows =
+        internal_tags
+        .order(Arel.sql('tags.post_count DESC, tag_names.name'))
+        .limit(20)
+        .map { |tag|
+          TagRepr.base(tag, language_code: locale.language_code)
+                 .merge(matched_alias: matched_alias_by_tag_id[tag.id])
+        }
 
-    render json: tags.map { |tag|
-      TagRepr.base(tag).merge(matched_alias: matched_alias_by_tag_name_id[tag.tag_name_id])
-    }
+    return render json: internal_rows unless with_nico
+
+    external_base = ExternalTag.all
+    external_base = external_base.where('post_count > 0') if present_only
+
+    external_rows =
+        external_base
+        .where("CONCAT(platform, ':', name) LIKE ? OR name LIKE ?", prefix, prefix)
+        .order(post_count: :desc, name: :asc)
+        .limit(20)
+        .map { external_tag_json(_1) }
+
+    rows =
+    (internal_rows + external_rows)
+        .sort_by { |row| [-row['post_count'], row['name'] || row[:name]] }
+        .first(20)
+
+    render json: rows
   end
 
   def show
-    tag = Tag.joins(:tag_name)
-             .includes(:tag_name, :materials, tag_name: :wiki_page)
-             .find_by(id: params[:id])
-    if tag
-      render json: TagRepr.base(tag)
-    else
-      head :not_found
-    end
+    locale = resolve_locale!
+
+    tag =
+        Tag
+        .joins(:tag_names)
+        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .find_by(id: params[:id],
+                 tag_names: { language_code: locale.language_code, primary_flg: true })
+    return render json: TagRepr.base(tag, language_code: locale.language_code) if tag
+
+    external_tag = ExternalTag.find_by(id: params[:id])
+    return render json: ExternalTagRepr.base(external_tag) if external_tag
+
+    head :not_found
   end
 
   def show_by_name
     name = params[:name].to_s.strip
     return render_bad_request('name は必須です．') if name.blank?
 
-    tag = Tag.joins(:tag_name)
-             .includes(:tag_name, :materials, tag_name: :wiki_page)
-             .find_by(tag_names: { name: })
-    if tag
-      render json: TagRepr.base(tag)
-    else
-      head :not_found
-    end
+    locale = resolve_locale!
+
+    tag =
+        Tag
+        .joins(:tag_names)
+        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
+    return render json: TagRepr.base(tag, language_code: locale.language_code) if tag
+
+    platform, external_name = name.split(':', 2)
+    return head :not_found unless external_name
+
+    external_tag = ExternalTag.find_by(platform:, name: external_name)
+    return head :not_found unless external_tag
+
+    render json: ExternalTagRepr.base(external_tag)
   end
 
   def deerjikists
-    tag = Tag.joins(:tag_name)
-             .includes(:tag_name, tag_name: :wiki_page)
-             .find_by(id: params[:id])
+    locale = resolve_locale!
+
+    tag = 
+        Tag.joins(:tag_names)
+        .includes(:tag_names, tag_names: :wiki_page)
+        .find_by(id: params[:id],
+                 tag_names: { language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
 
-    render json: { tag: TagRepr.base(tag),
-                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
+    render json: { tag: TagRepr.base(tag, language_code: locale.language_code),
+                   deerjikists: DeerjikistRepr.many(
+                       tag.deerjikists,
+                       language_code: locale.language_code) }
   end
 
   def deerjikists_by_name
     name = params[:name].to_s.strip
     return render_bad_request('name は必須です．') if name.blank?
 
-    tag = Tag.joins(:tag_name)
-             .includes(:tag_name, tag_name: :wiki_page)
-             .find_by(tag_names: { name: })
+    locale = resolve_locale!
+
+    tag =
+        Tag
+        .joins(:tag_names)
+        .includes(:tag_names, tag_names: :wiki_page)
+        .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
 
-    render json: { tag: TagRepr.base(tag),
-                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
+    render json: { tag: TagRepr.base(tag, language_code: locale.language_code),
+                   deerjikists: DeerjikistRepr.many(
+                       tag.deerjikists,
+                       language_code: locale.language_code) }
   end
 
   def update_deerjikists
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    tag = Tag.joins(:tag_name)
-             .includes(:tag_name, tag_name: :wiki_page)
-             .find_by(id: params[:id])
+    locale = resolve_locale!
+
+    tag =
+        Tag
+        .joins(:tag_names)
+        .includes(:tag_names, tag_names: :wiki_page)
+        .find_by(id: params[:id],
+                 tag_names: { language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
 
+    rows = normalise_deerjikist_rows(tag)
+    return if performed?
+
     ApplicationRecord.transaction do
-      tag.deerjikists = []
-      params[:_json].each.with_index do |item, i|
-        platform = item[:platform]
-        code = normalise_deerjikist_code(platform, item[:code])
-        deerjikist = Deerjikist.find_or_initialize_by(platform:, code:)
-        deerjikist.tag = tag
-        render_deerjikist_form_record_invalid(deerjikist, i) unless deerjikist.save
+      tag.lock!
+
+      requested_keys = rows.map { |row| [row[:platform], row[:code]] }.uniq
+      row_indexes_by_key = rows_by_key(rows)
+      locked_deerjikists = lock_deerjikists_for_tag_update(tag.id, requested_keys)
+      current_deerjikists = locked_deerjikists.filter { |deerjikist|
+        deerjikist.tag_id == tag.id
+      }
+      requested_deerjikists = locked_deerjikists.filter { |deerjikist|
+        row_indexes_by_key.key?([deerjikist.platform, deerjikist.code])
+      }
+
+      render_deerjikist_conflicts(locale, requested_deerjikists, row_indexes_by_key, tag)
+      raise ActiveRecord::Rollback if performed?
+
+      requested_keys_set = requested_keys.to_set
+      current_deerjikists.each do |deerjikist|
+        key = [deerjikist.platform, deerjikist.code]
+        deerjikist.destroy! unless requested_keys_set.include?(key)
+      end
+
+      existing_keys = requested_deerjikists.to_h { |deerjikist|
+        [[deerjikist.platform, deerjikist.code], true]
+      }
+      requested_keys.each do |platform, code|
+        next if existing_keys[[platform, code]]
+
+        deerjikist = Deerjikist.new(platform:, code:, tag:)
+        row_index = row_indexes_by_key[[platform, code]].first
+        begin
+          render_deerjikist_form_record_invalid(deerjikist, row_index) unless deerjikist.save
+        rescue ActiveRecord::RecordNotUnique
+          conflicts = lock_deerjikists_for_tag_update(tag.id, [[platform, code]])
+          render_deerjikist_conflicts(locale, conflicts, row_indexes_by_key, tag)
+        end
         raise ActiveRecord::Rollback if performed?
       end
     end
 
     return if performed?
 
-    render json: DeerjikistRepr.many(tag.reload.deerjikists)
+    render json: DeerjikistRepr.many(tag.reload.deerjikists,
+                                     language_code: locale.language_code)
   end
 
   def materials_by_name
     name = params[:name].to_s.strip
     return render_bad_request('name は必須です．') if name.blank?
+
+    locale = resolve_locale!
+
     material_filter = material_filter_param(default: 'any')
 
-    tag = Tag.joins(:tag_name)
-             .includes(:tag_name, :materials, tag_name: :wiki_page)
-             .find_by(tag_names: { name: })
+    tag =
+        Tag
+        .joins(:tag_names)
+        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
 
-    graph = build_with_depth_graph(material_filter)
+    graph = build_with_depth_graph(material_filter, locale.language_code)
 
-    render json: build_tag_children(tag, graph:)
+    render json: build_tag_children(tag, graph:, language_code: locale.language_code)
   end
 
   def update_all
@@ -245,39 +446,38 @@ class TagsController < ApplicationController
     return render_unprocessable_entity('カテゴリは必須です．', field: :category) if category.blank?
     return render_unprocessable_entity '廃止状態は必須です．', field: :deprecated unless params.key?(:deprecated)
 
-    return unless validate_tag_rename(tag, name)
+    locale = resolve_locale!
+
+    return unless validate_tag_rename(locale, tag, name)
 
     alias_names = params[:aliases].to_s.split.uniq
     parent_names = params[:parent_tags].to_s.split.uniq
     deprecated = bool?(:deprecated)
 
-    if tag.nico? && deprecated
-      return render_unprocessable_entity 'ニコタグは廃止できません．', field: :deprecated
-    end
-
-    if tag.nico? || category == 'nico'
+    if category == 'nico'
       return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
     end
 
     ApplicationRecord.transaction do
-      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user,
+                                     language_code: locale.language_code)
 
-      old_name = tag.name
+      old_name = tag.name(locale.language_code)
       name_changed = name != old_name
-      wiki_page = tag.tag_name.wiki_page if name_changed
+      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
 
       if tag.deprecated? == deprecated
         tag.update!(category:)
       else
         tag.update!(category:, deprecated_at: deprecated ? Time.current : nil)
       end
-      rename_tag_name!(tag, name) if name_changed
+      rename_tag_name!(locale, tag, name) if name_changed
 
-      alias_names << old_name if name_changed
+      alias_names << old_name if name_changed && old_name.present?
       alias_names.delete(name)
 
-      update_aliases!(tag, alias_names)
-      update_parent_tags!(tag, parent_names)
+      update_aliases!(locale, tag, alias_names)
+      update_parent_tags!(locale, tag, parent_names)
 
       tag.reload
 
@@ -285,17 +485,20 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
+          language_code: locale.language_code,
           name_changed:,
           wiki_page:)
     end
 
-    render json: TagRepr.base(tag.reload)
+    render json: TagRepr.base(tag.reload, language_code: locale.language_code)
   end
 
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
+
     name = params[:name].presence
     category = params[:category].presence
     deprecated_given = params.key?(:deprecated)
@@ -303,24 +506,21 @@ class TagsController < ApplicationController
 
     tag = Tag.find(params[:id])
 
-    if tag.nico? && deprecated_given && deprecated
-      return render_unprocessable_entity 'ニコタグは廃止できません．', field: :deprecated
-    end
+    return unless validate_tag_rename(locale, tag, name)
 
-    return unless validate_tag_rename(tag, name)
-
-    if tag.nico? || (category.present? && category == 'nico')
+    if category.present? && category == 'nico'
       return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
     end
 
     ApplicationRecord.transaction do
-      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user,
+                                     language_code: locale.language_code)
 
-      old_name = tag.name
+      old_name = tag.name(locale.language_code)
       name_changed = name.present? && name != old_name
-      wiki_page = tag.tag_name.wiki_page if name_changed
+      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
 
-      rename_tag_name!(tag, name) if name_changed
+      rename_tag_name!(locale, tag, name) if name_changed
       tag.update!(category:) if category.present?
       if deprecated_given && tag.deprecated? != deprecated
         tag.update!(deprecated_at: deprecated ? Time.current : nil)
@@ -332,11 +532,12 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
+          language_code: locale.language_code,
           name_changed:,
           wiki_page:)
     end
 
-    render json: TagRepr.base(tag.reload)
+    render json: TagRepr.base(tag.reload, language_code: locale.language_code)
   end
 
   private
@@ -348,7 +549,7 @@ class TagsController < ApplicationController
     value
   end
 
-  def build_with_depth_graph material_filter
+  def build_with_depth_graph material_filter, language_code
     children_by_parent_id = Hash.new { |h, k| h[k] = [] }
     parent_ids_by_child_id = Hash.new { |h, k| h[k] = [] }
 
@@ -363,10 +564,13 @@ class TagsController < ApplicationController
 
     material_tag_ids = Material.unscoped.kept.where.not(tag_id: nil).distinct.pluck(:tag_id).to_set
 
-    tags_by_id = Tag.joins(:tag_name)
-                    .where(id: tag_ids)
-                    .pluck('tags.id', 'tag_names.name', 'tags.category', 'tags.deprecated_at')
-                    .each_with_object({ }) do |(id, name, category, deprecated_at), h|
+    tags_by_id =
+        Tag
+        .joins(:tag_names)
+        .where(id: tag_ids,
+               tag_names: { language_code:, primary_flg: true })
+        .pluck('tags.id', 'tag_names.name', 'tags.category', 'tags.deprecated_at')
+        .each_with_object({ }) do |(id, name, category, deprecated_at), h|
       h[id] = { name:, category:, deprecated: deprecated_at.present?,
                 has_material: material_tag_ids.include?(id) }
     end
@@ -498,34 +702,33 @@ class TagsController < ApplicationController
       children: [] }
   end
 
-  def build_tag_children tag, graph: nil
+  def build_tag_children tag, graph: nil, language_code: 'ja'
     material = tag.materials.first
     tag_graph = graph && graph[:tags_by_id][tag.id]
     material =
         nil if tag_graph && !with_depth_visible_tag?(tag_graph, graph[:material_filter])
 
-    children = tag.children.sort_by(&:name)
+    children = tag.children.sort_by { _1.name(language_code) }
     if graph
       children = children.filter { |child_tag| visible_subtree?(child_tag.id, graph) }
     end
 
-    TagRepr.base(tag).merge(
-        children: children.map { build_tag_children(_1, graph:) },
+    TagRepr.base(tag, language_code:).merge(
+        children: children.map { build_tag_children(_1, graph:, language_code:) },
         has_material: tag_graph ? tag_graph[:has_material] : material.present?,
-        material: material && MaterialRepr.base(material, host: request.base_url))
+        material: material && MaterialRepr.base(
+            material,
+            host: request.base_url,
+            language_code:))
   end
 
-  def record_tag_version! tag, event_type:, created_by_user:, name_changed: false, wiki_page: nil
-    if tag.nico?
-      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
-      return
-    end
-
-    TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+  def record_tag_version! tag, event_type:, created_by_user:, language_code: 'ja',
+                          name_changed: false, wiki_page: nil
+    TagVersionRecorder.record!(tag:, event_type:, created_by_user:, language_code:)
 
     return unless name_changed
 
-    wiki_page ||= tag.tag_name.wiki_page
+    wiki_page ||= tag.tag_name('ja')&.wiki_page
     return unless wiki_page&.wiki_versions&.exists?
 
     WikiVersionRecorder.record!(
@@ -534,109 +737,140 @@ class TagsController < ApplicationController
         created_by_user:)
   end
 
-  def validate_tag_rename tag, name
-    return true if name.blank? || name == tag.name
+  def validate_tag_rename locale, tag, name
+    return true if name.blank? || name == tag.name(locale.language_code)
 
-    if tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
+    system_tag_names = ['タグ希望', 'bot操作', 'ニジラー情報不詳', '動画', 'ニコニコ']
+    if TagName.exists?(tag_id: tag.id,
+                       language_code: 'ja',
+                       primary_flg: true,
+                       name: system_tag_names)
       render_unprocessable_entity 'システム・タグの名称は変更できません．', field: :name
       return false
     end
 
-    target_tag_name = TagName.with_discarded.find_by(name:)
-    return true if target_tag_name.nil?
-    return true if target_tag_name.canonical_id?
+    target_tag_name = TagName.find_by(language_code: locale.language_code, name:)
+    return true unless target_tag_name&.primary_flg
 
     render_unprocessable_entity 'その名前は既に使はれてゐます．', field: :name
     false
   end
 
-  def rename_tag_name! tag, name
-    return if name == tag.name
+  def rename_tag_name! locale, tag, name
+    return if name == tag.name(locale.language_code)
 
-    current_tag_name = tag.tag_name
-    target_tag_name = TagName.with_discarded.find_by(name:)
+    current_tag_name = tag.tag_name(locale.language_code)
+    target_tag_name = TagName.find_by(language_code: locale.language_code, name:)
 
-    if target_tag_name.nil?
-      current_tag_name.update!(name:)
+    unless target_tag_name
+      if current_tag_name
+        current_tag_name.update!(name:, auto_generated: false)
+      else
+        current_tag_name = TagName.create!(
+            tag:,
+            language_code: locale.language_code,
+            script_code: locale.script_code,
+            name:,
+            primary_flg: true)
+        tag.association(:tag_names).reset
+      end
       return
     end
 
-    promote_tag_alias!(
-        tag,
-        current_tag_name:,
-        promoted_tag_name: target_tag_name)
+    promote_tag_alias!(tag, current_tag_name:, promoted_tag_name: target_tag_name)
   end
 
   def promote_tag_alias! tag, current_tag_name:, promoted_tag_name:
-    old_owner_tag = promoted_tag_name.canonical&.tag
+    old_owner_tag = promoted_tag_name.tag
 
     if old_owner_tag && old_owner_tag != tag
       TagVersioning.ensure_snapshot!(old_owner_tag, created_by_user: current_user)
     end
 
-    promoted_tag_name.undiscard! if promoted_tag_name.discarded?
-    promoted_tag_name.update!(canonical: nil)
+    current_tag_name.wiki_page&.update!(tag_name_id: promoted_tag_name.id)
+    current_tag_name.association(:wiki_page).reset
 
-    TagName.with_discarded
-           .where(canonical_id: current_tag_name.id)
+    current_tag_name.update!(canonical_id: promoted_tag_name.id,
+                             primary_flg: false, auto_generated: false)
+    promoted_tag_name.update!(tag:, canonical_id: nil, primary_flg: true, auto_generated: false)
+
+    TagName.where(tag:,
+                  language_code: current_tag_name.language_code,
+                  primary_flg: false)
            .where.not(id: promoted_tag_name.id)
            .find_each do |alias_tag_name|
-      alias_tag_name.update!(canonical: promoted_tag_name)
+      alias_tag_name.update!(canonical_id: promoted_tag_name.id, primary_flg: false)
     end
 
-    current_tag_name.wiki_page&.update!(tag_name: promoted_tag_name)
-    tag.update!(tag_name: promoted_tag_name)
+    tag.update!(tag_name_id: promoted_tag_name.id)
     current_tag_name.association(:wiki_page).reset
     current_tag_name.association(:tag).reset
-    current_tag_name.reload.update!(canonical: promoted_tag_name)
+    current_tag_name.reload.update!(canonical_id: promoted_tag_name.id, primary_flg: false)
 
     return unless old_owner_tag && old_owner_tag != tag
 
-    record_tag_version!(old_owner_tag.reload, event_type: :update, created_by_user: current_user)
+    record_tag_version!(old_owner_tag.reload, event_type: :update,
+                        created_by_user: current_user,
+                        language_code: current_tag_name.language_code)
   end
 
-  def update_aliases! tag, alias_names
+  def update_aliases! locale, tag, alias_names
     alias_names = alias_names.uniq
 
     affected_tags = [tag]
 
-    current_aliases = tag.tag_name.aliases.to_a
+    primary_tag_name = TagName.find_by!(tag:,
+                                        language_code: locale.language_code,
+                                        primary_flg: true)
+    current_aliases = tag.tag_names.where(language_code: locale.language_code,
+                                          primary_flg: false).to_a
 
     current_aliases.each do |alias_tag_name|
       next if alias_names.include?(alias_tag_name.name)
 
-      affected_tags << alias_tag_name.canonical&.tag
+      affected_tags << alias_tag_name.tag
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
-      affected_tags << alias_tag_name.canonical&.tag
+      alias_tag_name = TagName.find_by(language_code: locale.language_code, name: alias_name)
+      if alias_tag_name&.primary? && alias_tag_name.tag_id && alias_tag_name.tag_id != tag.id
+        alias_tag_name.errors.add(:name, 'その名前は既に使はれてゐます．')
+        raise ActiveRecord::RecordInvalid, alias_tag_name
+      end
+      affected_tags << alias_tag_name&.tag
     end
 
     affected_tags.compact.uniq.each do |affected_tag|
-      TagVersioning.ensure_snapshot!(affected_tag, created_by_user: current_user)
+      TagVersioning.ensure_snapshot!(affected_tag, created_by_user: current_user,
+                                     language_code: locale.language_code)
     end
 
     current_aliases.each do |alias_tag_name|
       next if alias_names.include?(alias_tag_name.name)
 
-      alias_tag_name.update!(canonical: nil)
+      alias_tag_name.update!(canonical_id: nil, tag_id: nil)
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
-      alias_tag_name.update!(canonical: tag.tag_name)
+      alias_tag_name = TagName.find_or_initialize_by(
+          language_code: locale.language_code,
+          name: alias_name)
+      alias_tag_name.script_code = locale.script_code
+      alias_tag_name.update!(tag:, primary_flg: false, auto_generated: false,
+                             canonical_id: primary_tag_name.id)
     end
 
     affected_tags.compact.uniq.each do |affected_tag|
-      record_tag_version!(affected_tag, event_type: :update, created_by_user: current_user)
+      record_tag_version!(affected_tag, event_type: :update,
+                          created_by_user: current_user,
+                          language_code: locale.language_code)
     end
   end
 
-  def update_parent_tags! tag, parent_names
-    parent_tags = Tag.normalise_tags!(parent_names, with_tagme: false,
-                                                    with_no_deerjikist: false,
-                                                    deny_nico: true)
+  def update_parent_tags! locale, tag, parent_names
+    parent_tags = Tag.normalise_tags!(locale, parent_names,
+                                      with_tagme: false,
+                                      with_no_deerjikist: false)
 
     old_parent_tags = tag.parents.to_a
 
@@ -653,6 +887,7 @@ class TagsController < ApplicationController
   end
 
   def normalise_deerjikist_code platform, code
+    code = code.to_s
     return code if platform != 'youtube' || code[0] != '@'
 
     url = "https://www.youtube.com/#{ code }"
@@ -669,6 +904,84 @@ class TagsController < ApplicationController
     nil
   end
 
+  def normalise_deerjikist_rows tag
+    rows = []
+
+    params[:_json].each.with_index do |item, index|
+      platform = item[:platform]
+      unless Deerjikist.platforms.key?(platform)
+        render_deerjikist_platform_invalid(index)
+        return rows
+      end
+
+      code = normalise_deerjikist_code(platform, item[:code])
+      deerjikist = Deerjikist.new(platform:, code:, tag:)
+      unless deerjikist.valid?
+        render_deerjikist_form_record_invalid(deerjikist, index)
+        return rows
+      end
+
+      rows << { index:, platform:, code: }
+    end
+
+    rows
+  end
+
+  def lock_deerjikists_for_tag_update tag_id, keys
+    clauses = ['tag_id = ?']
+    values = [tag_id]
+
+    keys.each do |platform, code|
+      clauses << '(platform = ? AND code = ?)'
+      values << platform << code
+    end
+
+    Deerjikist
+      .where(clauses.join(' OR '), *values)
+      .order(:platform, :code)
+      .lock
+      .to_a
+  end
+
+  def render_deerjikist_conflicts locale, deerjikists, row_indexes_by_key, tag
+    conflicts = deerjikists.filter { |deerjikist| deerjikist.tag_id != tag.id }
+    return if conflicts.empty?
+
+    tag_names_by_id =
+        Tag
+        .joins(:tag_names)
+        .where(tag_names: { language_code: locale.language_code, primary_flg: true },
+               id: conflicts.map(&:tag_id).uniq)
+        .pluck('tags.id', 'tag_names.name')
+        .to_h
+    fields = { }
+
+    conflicts.each do |deerjikist|
+      message = "この情報は既に「#{ tag_names_by_id[deerjikist.tag_id] }」に紐づいてゐます．"
+      row_indexes_by_key[[deerjikist.platform, deerjikist.code]].each do |index|
+        field = :"deerjikists.#{ index }.code"
+        fields[field] ||= []
+        fields[field] << message
+      end
+    end
+
+    render_validation_error fields:
+  end
+
+  def render_deerjikist_platform_invalid index
+    render_validation_error fields: {
+      :"deerjikists.#{ index }.platform" => ['値が不正です．'],
+    }
+  end
+
+  def rows_by_key rows
+    rows.each_with_object({ }) do |row, result|
+      key = [row[:platform], row[:code]]
+      result[key] ||= []
+      result[key] << row[:index]
+    end
+  end
+
   def render_deerjikist_form_record_invalid deerjikist, index
     fields = { }
 
@@ -687,4 +1000,20 @@ class TagsController < ApplicationController
 
     render_validation_error fields:
   end
+
+  def external_tag_json tag
+    { 'id' => tag.id,
+      'name' => "#{ tag.platform }:#{ tag.name }",
+      'category' => 'nico',
+      'deprecated_at' => nil,
+      'created_at' => tag.created_at,
+      'updated_at' => tag.created_at,
+      'post_count' => tag.post_count,
+      'matched_alias' => nil,
+      'aliases' => [],
+      'parents' => [],
+      'has_wiki' => false,
+      'material_id' => nil,
+      'has_deerjikists' => false }
+  end
 end

backend/app/controllers/theatre_skip_events_controller.rb

@@ -6,7 +6,7 @@ class TheatreSkipEventsController < ApplicationController
     events =
         TheatreSkipEvent
         .where(theatre_id: params[:theatre_id])
-        .includes(:post, tags: :tag_name)
+        .includes(:post, tags: :tag_names)
         .order(created_at: :desc)
         .limit(limit)
 
@@ -14,7 +14,7 @@ class TheatreSkipEventsController < ApplicationController
       { id: event.id,
         theatre_id: event.theatre_id,
         post: { id: event.post.id, title: event.post.title, url: event.post.url },
-        tags: event.tags.map { |tag| { id: tag.id, name: tag.name } },
+        tags: event.tags.map { |tag| { id: tag.id, name: tag.name('ja') } },
         programme_position: event.programme_position,
         created_at: event.created_at }
     }

backend/app/controllers/wiki_pages_controller.rb

@@ -94,7 +94,11 @@ class WikiPagesController < ApplicationController
     return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
     return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
-    tag_name = TagName.find_undiscard_or_create_by!(name: title)
+    tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
+      name.script_code = 'Jpan'
+      name.primary_flg = true
+      name.auto_generated = false
+    end
 
     page =
         Wiki::Commit.create_content!(

backend/app/models/external_tag.rb

@@ -0,0 +1,24 @@
+class ExternalTag < ApplicationRecord
+  enum :platform, nico: 'nico'
+  validates :platform, presence: true, inclusion: { in: ExternalTag.platforms.keys }
+
+  has_many :post_external_tags, dependent: :delete_all
+  has_many :posts, through: :post_external_tags
+
+  has_many :nico_tag_versions, foreign_key: :tag_id, inverse_of: :external_tag
+
+  has_many :nico_tag_relations,
+           foreign_key: :nico_tag_id,
+           inverse_of: :nico_tag,
+           dependent: :destroy
+
+  has_many :linked_tags, through: :nico_tag_relations, source: :tag
+
+  def snapshot_linked_tag_names language_code = 'ja'
+    linked_tags
+        .joins(:tag_names)
+        .where(tag_names: { language_code:, primary_flg: true })
+        .order('tag_names.name')
+        .pluck('tag_names.name')
+  end
+end

backend/app/models/language.rb

@@ -0,0 +1,5 @@
+class Language < ApplicationRecord
+  has_many :locales, foreign_key: :language_code, primary_key: :code
+
+  enum :code, ja: 'ja'
+end

backend/app/models/locale.rb

@@ -0,0 +1,27 @@
+class Locale < ApplicationRecord
+  after_create_commit :generate_tag_names!
+
+  belongs_to :language, foreign_key: :language_code, primary_key: :code
+  belongs_to :script, foreign_key: :script_code, primary_key: :code
+
+  enum :code, ja: 'ja', en: 'en', fr: 'fr'
+
+  def self.nipponese = Locale.find('ja')
+
+  private
+
+  def generate_tag_names!
+    ApplicationRecord.transaction do
+      tag_ids = TagName.where(language_code:, primary_flg: true).pluck(:tag_id)
+      Tag.where.not(id: tag_ids).find_each do
+        TagName.create!(tag_id: _1.id,
+                        language_code:,
+                        name: TagName.generate_name(self, _1, _1.tag_name('ja')),
+                        script_code:,
+                        primary_flg: true,
+                        auto_generated: true,
+                        canonical_id: nil)
+      end
+    end
+  end
+end

backend/app/models/nico_tag_relation.rb

@@ -1,24 +1,10 @@
 class NicoTagRelation < ApplicationRecord
-  belongs_to :nico_tag, class_name: 'Tag'
-  belongs_to :tag, class_name: 'Tag'
+  belongs_to :nico_tag,
+             class_name: 'ExternalTag',
+             foreign_key: :nico_tag_id,
+             inverse_of: :nico_tag_relations
+  belongs_to :tag, class_name: 'Tag', foreign_key: :tag_id
 
   validates :nico_tag_id, presence: true
   validates :tag_id, presence: true
-
-  validate :nico_tag_must_be_nico
-  validate :tag_mustnt_be_nico
-
-  private
-
-  def nico_tag_must_be_nico
-    if nico_tag && nico_tag.category != 'nico'
-      errors.add :nico_tag_id, 'タグのカテゴリがニコニコである必要があります．'
-    end
-  end
-
-  def tag_mustnt_be_nico
-    if tag && tag.category == 'nico'
-      errors.add :tag_id, '連携先タグのカテゴリはニコニコであってはなりません．'
-    end
-  end
 end

backend/app/models/nico_tag_version.rb

@@ -1,7 +1,7 @@
 class NicoTagVersion < ApplicationRecord
   include VersionRecord
 
-  belongs_to :tag
+  belongs_to :external_tag, foreign_key: :tag_id, inverse_of: :nico_tag_versions
 
   validates :name, presence: true
 end

backend/app/models/post.rb

@@ -55,25 +55,27 @@ class Post < ApplicationRecord
   belongs_to :uploaded_user, class_name: 'User', optional: true
 
   has_many :post_tags, dependent: :destroy, inverse_of: :post
-  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :post
-  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
-  has_many :tags, through: :active_post_tags
+  has_many :tags, through: :post_tags
   has_many :active_tags, -> { where(tags: { deprecated_at: nil }) },
-           through: :active_post_tags, source: :tag
+           through: :post_tags,
+           source: :tag
 
   has_many :user_post_views, dependent: :delete_all
   has_many :post_similarities, dependent: :delete_all
   has_many :post_versions
+
   has_many :gekanator_guessed_games,
            class_name: 'GekanatorGame',
            foreign_key: :guessed_post_id,
            dependent: :delete_all,
            inverse_of: :guessed_post
+
   has_many :gekanator_correct_games,
            class_name: 'GekanatorGame',
            foreign_key: :correct_post_id,
            dependent: :delete_all,
            inverse_of: :correct_post
+
   has_many :gekanator_question_examples, dependent: :delete_all
 
   has_many :parent_post_implications,
@@ -90,6 +92,9 @@ class Post < ApplicationRecord
            inverse_of: :parent_post
   has_many :children, through: :child_post_implications, source: :post
 
+  has_many :post_external_tags, dependent: :destroy
+  has_many :external_tags, through: :post_external_tags
+
   has_one_attached :thumbnail
 
   attribute :version_no, :integer, default: 1
@@ -121,14 +126,14 @@ class Post < ApplicationRecord
     super(options).merge(thumbnail: nil)
   end
 
-  def snapshot_tag_names
+  def snapshot_tag_names language_code = 'ja'
     post_tags
-        .kept
-        .joins(tag: :tag_name)
-        .includes(:sections, tag: :tag_name)
+        .joins(tag: :tag_names)
+        .where(tag_names: { language_code:, primary_flg: true })
+        .includes(:sections, tag: :tag_names)
         .order('tag_names.name')
         .map do |post_tag|
-      name = post_tag.tag.tag_name.name
+      name = post_tag.tag.name(language_code)
       sections = post_tag.sections.sort_by(&:begin_ms)
 
       next name if sections.empty?
@@ -137,8 +142,47 @@ class Post < ApplicationRecord
     end
   end
 
+  def self.tag_snapshot_literal tag
+    sections = tag.fetch('sections', []).map do |sec|
+      begin_ms = sec.fetch('begin_ms')
+      end_ms = sec['end_ms']
+
+      "[#{ Post.ms_to_time(begin_ms) }-#{ end_ms ? Post.ms_to_time(end_ms) : '' }]"
+    end
+
+    "#{ tag.fetch('name') }#{ sections.join }"
+  end
+
+  def snapshot_tags_json language_code = 'ja'
+    tag_snapshots =
+        post_tags
+            .joins(tag: :tag_names)
+            .where(tag_names: { language_code:, primary_flg: true })
+            .includes(:sections, tag: :tag_names)
+            .order('tags.id')
+            .map { |pt|
+          { 'tag_id' => pt.tag.id,
+            'version_no' => pt.tag.version_no,
+            'name' => pt.tag.name(language_code),
+            'category' => pt.tag.category,
+            'sections' => pt.sections.sort_by(&:begin_ms).map {
+                            { 'begin_ms' => _1.begin_ms, 'end_ms' => _1.end_ms }
+                          } }
+        }
+
+    external_tag_snapshots =
+        post_external_tags.order(:external_tag_id).map {
+          { 'external_tag_id' => _1.external_tag_id }
+        }
+
+    tag_snapshots + external_tag_snapshots
+  end
+
   def self.section_literal section
-    "[#{ Post.ms_to_time(section.begin_ms) }-#{ section.end_ms ? Post.ms_to_time(section.end_ms) : '' }]"
+    end_ms =
+        section.end_ms ? Post.ms_to_time(section.end_ms) : ''
+
+    "[#{ Post.ms_to_time(section.begin_ms) }-#{ end_ms }]"
   end
 
   def self.ms_to_time ms
@@ -323,7 +367,9 @@ class Post < ApplicationRecord
   end
 
   def self.external_svg_reference?(attribute_name, attribute_value)
-    return external_svg_url?(attribute_value) if ['href', 'xlink:href', 'src'].include?(attribute_name)
+    if ['href', 'xlink:href', 'src'].include?(attribute_name)
+      return external_svg_url?(attribute_value)
+    end
     return style_contains_disallowed_urls?(attribute_value) if attribute_name == 'style'
     return svg_url_function_disallowed?(attribute_value) if attribute_value.match?(/url\s*\(/i)
 
@@ -344,7 +390,12 @@ class Post < ApplicationRecord
 
   def self.svg_url_function_disallowed?(value)
     value.to_s.scan(/url\s*\(([^)]*)\)/i).flatten.any? do |entry|
-      reference = entry.to_s.strip.delete_prefix("'").delete_prefix('"').delete_suffix("'").delete_suffix('"')
+      reference =
+          entry.to_s.strip
+               .delete_prefix("'")
+               .delete_prefix('"')
+               .delete_suffix("'")
+               .delete_suffix('"')
       reference.present? && !(reference.start_with?('#'))
     end
   end
@@ -433,7 +484,12 @@ class Post < ApplicationRecord
 
     match =
         value.match(
-            /\A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})(?::(\d{2})(?:\.(\d+))?)?(Z|[+-]\d{2}:?\d{2})?\z/)
+            /
+              \A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})
+              (?::(\d{2})(?:\.(\d+))?)?
+              (Z|[+-]\d{2}:?\d{2})?
+              \z
+            /x)
     return nil if match.nil?
 
     year = match[1].to_i

backend/app/models/post_external_tag.rb

@@ -0,0 +1,4 @@
+class PostExternalTag < ApplicationRecord
+  belongs_to :post
+  belongs_to :external_tag, counter_cache: :post_count
+end

backend/app/models/post_tag.rb

@@ -1,14 +1,7 @@
 class PostTag < ApplicationRecord
-  include Discard::Model
-
-  before_destroy do
-    raise ActiveRecord::ReadOnlyRecord, '消さないでください．'
-  end
-
   belongs_to :post
   belongs_to :tag, counter_cache: :post_count
   belongs_to :created_user, class_name: 'User', optional: true
-  belongs_to :deleted_user, class_name: 'User', optional: true
 
   has_many :sections, -> { order(:begin_ms) }, class_name: 'PostTagSection',
                                                foreign_key: [:post_id, :tag_id],
@@ -18,18 +11,5 @@ class PostTag < ApplicationRecord
 
   validates :post_id, presence: true
   validates :tag_id, presence: true
-  validates :post_id, uniqueness: {
-      scope: :tag_id,
-      conditions: -> { where(discarded_at: nil) } }
-
-  def discard_by! deleted_user
-    return self if discarded?
-
-    transaction do
-      update!(discarded_at: Time.current, deleted_user:)
-      Tag.where(id: tag_id).update_all('post_count = GREATEST(post_count - 1, 0)')
-    end
-
-    self
-  end
+  validates :post_id, uniqueness: { scope: :tag_id }
 end

backend/app/models/post_tag_section.rb

@@ -4,10 +4,10 @@ class PostTagSection < ApplicationRecord
   belongs_to :post
   belongs_to :tag
 
-  belongs_to :post_tag, -> { kept }, foreign_key: [:post_id, :tag_id],
-                                     primary_key: [:post_id, :tag_id],
-                                     inverse_of: :sections,
-                                     optional: true
+  belongs_to :post_tag, foreign_key: [:post_id, :tag_id],
+                        primary_key: [:post_id, :tag_id],
+                        inverse_of: :sections,
+                        optional: true
 
   validates :post_id, presence: true
   validates :tag_id, presence: true

backend/app/models/region.rb

@@ -0,0 +1,3 @@
+class Region < ApplicationRecord
+  ;
+end

backend/app/models/script.rb

@@ -0,0 +1,5 @@
+class Script < ApplicationRecord
+  has_many :locales, foreign_key: :script_code, primary_key: :code
+
+  enum :code, Jpan: 'Jpan'
+end

backend/app/models/tag.rb

@@ -2,8 +2,6 @@ require 'set'
 
 
 class Tag < ApplicationRecord
-  include MyDiscard
-
   class NicoTagNormalisationError < ArgumentError
     ;
   end
@@ -28,15 +26,12 @@ class Tag < ApplicationRecord
   end
 
   has_many :post_tags, inverse_of: :tag
-  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
-  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
-  has_many :posts, through: :active_post_tags
-
-  has_many :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
-  has_many :linked_tags, through: :nico_tag_relations, source: :tag
+  has_many :posts, through: :post_tags
 
   has_many :reversed_nico_tag_relations,
-           class_name: 'NicoTagRelation', foreign_key: :tag_id, dependent: :destroy
+           class_name: 'NicoTagRelation',
+           foreign_key: :tag_id,
+           dependent: :destroy
   has_many :linked_nico_tags, through: :reversed_nico_tag_relations, source: :nico_tag
 
   has_many :tag_implications, foreign_key: :parent_tag_id, dependent: :destroy
@@ -54,32 +49,22 @@ class Tag < ApplicationRecord
   has_many :materials
 
   has_many :tag_versions
-  has_many :nico_tag_versions
 
-  belongs_to :tag_name
-  delegate :wiki_page, to: :tag_name
+  has_many :tag_names
 
   attribute :version_no, :integer, default: 1
 
-  delegate :name, to: :tag_name, allow_nil: true
-  validates :tag_name, presence: true
-
   enum :category, deerjikist:  'deerjikist',
                   meme:        'meme',
                   character:   'character',
                   general:     'general',
                   material:    'material',
-                  nico:        'nico',
                   meta:        'meta'
 
   validates :category, presence: true, inclusion: { in: Tag.categories.keys }
 
-  validate :nico_tag_name_must_start_with_nico
-  validate :tag_name_must_be_canonical
   validate :category_must_be_deerjikist_with_deerjikists
-  validate :nico_tags_cannot_be_deprecated
-
-  scope :nico_tags, -> { nico }
+  validate :tag_names_must_be_valid
 
   CATEGORY_PREFIXES = {
       'general:'    => :general,
@@ -93,8 +78,20 @@ class Tag < ApplicationRecord
       'mtr:'        => :material,
       'meta:'       => :meta }.freeze
 
-  def name= val
-    (self.tag_name ||= build_tag_name).name = val
+  SYSTEM_TAG_NAMES = ['タグ希望', 'bot操作', 'ニジラー情報不詳', '動画', 'ニコニコ', 'YouTube'].freeze
+
+  def tag_name language_code
+    if tag_names.loaded?
+      tag_names.find { _1.language_code == language_code && _1.primary_flg }
+    else
+      tag_names.find_by(language_code:, primary_flg: true)
+    end
+  end
+  def name(language_code) = tag_name(language_code)&.name
+  def wiki_page = tag_name('ja')&.wiki_page
+
+  def system?
+    tag_name('ja')&.name.in?(SYSTEM_TAG_NAMES)
   end
 
   def deprecated? = deprecated_at?
@@ -105,221 +102,285 @@ class Tag < ApplicationRecord
 
   def has_deerjikists = deerjikists.loaded? ? deerjikists.any? : deerjikists.exists?
 
-  def self.tagme = find_or_create_by_tag_name!('タグ希望', category: :meta)
-  def self.bot = find_or_create_by_tag_name!('bot操作', category: :meta)
-  def self.no_deerjikist = find_or_create_by_tag_name!('ニジラー情報不詳', category: :meta)
-  def self.video = find_or_create_by_tag_name!('動画', category: :meta)
-  def self.niconico = find_or_create_by_tag_name!('ニコニコ', category: :meta)
-  def self.youtube = find_or_create_by_tag_name!('YouTube', category: :meta)
-
-  def self.normalise_tags! tag_names, with_tagme: true,
-                                      with_no_deerjikist: true,
-                                      deny_nico: true,
-                                      deny_deprecated: false,
-                                      with_sections: false
-    if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
-      raise NicoTagNormalisationError
-    end
-
-    sections = { }
-    tags = tag_names.map do |name|
-      raw_name = name
-      pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
-
-      name = name.sub(/\A#{ pf }/i, '')
-
-      sections_by_tag = []
-      while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
-        name = "#{ match[1] }#{ match[4] }"
-        next if match[2].empty? && match[3].empty?
-
-        sections_by_tag << normalise_section_range!(
-            begin_raw: match[2],
-            end_raw: match[3],
-            tag_name: name)
-      end
-
-      if name.include?('[') || name.include?(']')
-        raise SectionLiteralParseError.new(raw_name, raw_name)
-      end
-
-      name = TagName.canonicalise(name).first
-
-      find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
-        if deny_deprecated && tag.deprecated?
-          raise DeprecatedTagNormalisationError, [tag.name]
-        end
-
-        tag.update!(category: cat) if cat && tag.category != cat
-        next if sections_by_tag.empty?
-
-        sections[tag.id] ||= []
-        sections[tag.id].concat(sections_by_tag)
-        sections[tag.id] = merge_section_ranges(sections[tag.id])
-        sections.delete(tag.id) if sections[tag.id] == [[0, nil]]
-      end
-    end
-
-    tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
-    tags << Tag.no_deerjikist if with_no_deerjikist && tags.all? { |t| !(t.deerjikist?) }
-    tags.uniq!(&:id)
-
-    if with_sections
-      { tags:, sections: }
-    else
-      tags
-    end
+  def snapshot_aliases(language_code)
+    tag_names.where(language_code:, primary_flg: false).order(:name).pluck(:name)
   end
 
-  def self.expand_parent_tags tags
-    return [] if tags.blank?
-
-    seen = Set.new
-    result = []
-    stack = tags.compact.dup
-
-    until stack.empty?
-      tag = stack.pop
-      next unless tag
-
-      tag.parents.each do |parent|
-        next if seen.include?(parent.id)
-
-        seen << parent.id
-        result << parent
-        stack << parent
-      end
-    end
-
-    (result + tags).uniq { |t| t.id }
-  end
-
-  def self.normalise_section_range! begin_raw:, end_raw:, tag_name:
-    begin_ms = begin_raw.empty? ? 0 : time_to_ms!(begin_raw, tag_name:)
-    end_ms = end_raw.empty? ? nil : time_to_ms!(end_raw, tag_name:)
-
-    if end_ms
-      begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
-      end_ms = begin_ms + 1 if begin_ms == end_ms
-    end
-
-    [begin_ms, end_ms]
-  end
-
-  def self.merge_section_ranges ranges
-    sorted_ranges = ranges.sort_by { |begin_ms, end_ms| [begin_ms, end_ms || Float::INFINITY] }
-    merged = []
-
-    sorted_ranges.each do |begin_ms, end_ms|
-      if merged.empty?
-        merged << [begin_ms, end_ms]
-        next
-      end
-
-      last_begin_ms, last_end_ms = merged[-1]
-      if last_end_ms.nil? || begin_ms <= last_end_ms
-        merged[-1] = [last_begin_ms, merge_section_end(last_end_ms, end_ms)]
-      else
-        merged << [begin_ms, end_ms]
-      end
-    end
-
-    merged
-  end
-
-  def self.merge_section_end left_end_ms, right_end_ms
-    return nil if left_end_ms.nil? || right_end_ms.nil?
-
-    [left_end_ms, right_end_ms].max
-  end
-
-  def self.find_or_create_by_tag_name! name, category:
-    tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
-    tn = tn.canonical if tn.canonical_id?
-
-    Tag.find_undiscard_or_create_by!(tag_name_id: tn.id) do |t|
-      t.category = category
-    end
-  rescue ActiveRecord::RecordNotUnique
-    retry
-  end
-
-  def self.merge_tags! target_tag, source_tags, created_by_user: nil
-    target_tag => Tag
-
-    affected_post_ids = Set.new
-
-    Tag.transaction do
-      TagVersioning.ensure_snapshot!(target_tag, created_by_user:)
-
-      Array(source_tags).compact.uniq.each do |source_tag|
-        source_tag => Tag
-
-        next if source_tag == target_tag
-
-        TagVersioning.ensure_snapshot!(source_tag, created_by_user:)
-
-        source_tag.post_tags.kept.find_each do |source_pt|
-          post_id = source_pt.post_id
-          affected_post_ids << post_id
-          source_pt.discard_by!(created_by_user)
-          unless PostTag.kept.exists?(post_id:, tag: target_tag)
-            PostTag.create!(post_id:, tag: target_tag)
-          end
-        end
-
-        source_tag_name = source_tag.tag_name
-
-        if source_tag_name.wiki_page.present?
-          raise ActiveRecord::RecordInvalid.new(source_tag_name)
-        end
-
-        TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
-        source_tag.discard!
-
-        if source_tag.nico?
-          source_tag_name.discard!
-        else
-          source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
-                                         updated_at: Time.current)
-        end
-
-        TagVersioning.record!(target_tag, event_type: :update, created_by_user:)
-      end
-
-      Post.where(id: affected_post_ids.to_a).find_each do |post|
-        PostVersionRecorder.ensure_snapshot!(post, created_by_user:)
-        PostVersionRecorder.record!(post:, event_type: :update, created_by_user:)
-      end
-
-      # 投稿件数を再集計
-      target_tag.update_columns(post_count: PostTag.kept.where(tag: target_tag).count)
-    end
-
-    target_tag.reload
-  end
-
-  def snapshot_aliases = tag_name.aliases.kept.order(:name).pluck(:name)
-
   def snapshot_parent_tag_ids = parents.order(:id).pluck(:id)
 
-  def snapshot_linked_tag_names
-    linked_tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  def snapshot_linked_tag_names language_code
+    linked_tags
+        .joins(:tag_names)
+        .where(tag_names: { language_code:, primary_flg: true })
+        .order('tag_names.name')
+        .pluck('tag_names.name')
+  end
+
+  class << self
+    def tagme = find_or_create_by_tag_name!(Locale.nipponese, 'タグ希望', category: :meta)
+    def bot = find_or_create_by_tag_name!(Locale.nipponese, 'bot操作', category: :meta)
+    def no_deerjikist =
+        find_or_create_by_tag_name!(Locale.nipponese, 'ニジラー情報不詳', category: :meta)
+    def video = find_or_create_by_tag_name!(Locale.nipponese, '動画', category: :meta)
+    def niconico = find_or_create_by_tag_name!(Locale.nipponese, 'ニコニコ', category: :meta)
+    def youtube = find_or_create_by_tag_name!(Locale.nipponese, 'YouTube', category: :meta)
+
+    def normalise_tags! locale, tag_names,
+                             with_tagme: true,
+                             with_no_deerjikist: true,
+                             deny_deprecated: false,
+                             with_sections: false
+      if tag_names.any? { |n| n.downcase.start_with?('nico:') }
+        raise NicoTagNormalisationError
+      end
+
+      sections = { }
+      tags = tag_names.map do |name|
+        raw_name = name
+        pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
+
+        name = name.sub(/\A#{ pf }/i, '')
+
+        sections_by_tag = []
+        while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
+          name = "#{ match[1] }#{ match[4] }"
+          next if match[2].empty? && match[3].empty?
+
+          sections_by_tag << normalise_section_range!(
+              begin_raw: match[2],
+              end_raw: match[3],
+              tag_name: name)
+        end
+
+        if name.include?('[') || name.include?(']')
+          raise SectionLiteralParseError.new(raw_name, raw_name)
+        end
+
+        name = TagName.canonicalise(locale, name).first
+
+        find_or_create_by_tag_name!(locale, name, category: (cat || :general)).tap do |tag|
+          if deny_deprecated && tag.deprecated?
+            raise DeprecatedTagNormalisationError, [tag.name(locale.language_code)]
+          end
+
+          tag.update!(category: cat) if cat && tag.category != cat
+          next if sections_by_tag.empty?
+
+          sections[tag.id] ||= []
+          sections[tag.id].concat(sections_by_tag)
+          sections[tag.id] = merge_section_ranges(sections[tag.id])
+          sections.delete(tag.id) if sections[tag.id] == [[0, nil]]
+        end
+      end
+
+      tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
+      tags << Tag.no_deerjikist if with_no_deerjikist && tags.all? { |t| !(t.deerjikist?) }
+      tags.uniq!(&:id)
+
+      if with_sections
+        { tags:, sections: }
+      else
+        tags
+      end
+    end
+
+    def expand_parent_tags tags
+      return [] if tags.blank?
+
+      seen = Set.new
+      result = []
+      stack = tags.compact.dup
+
+      until stack.empty?
+        tag = stack.pop
+        next unless tag
+
+        tag.parents.each do |parent|
+          next if seen.include?(parent.id)
+
+          seen << parent.id
+          result << parent
+          stack << parent
+        end
+      end
+
+      (result + tags).uniq { |t| t.id }
+    end
+
+    def normalise_section_range! begin_raw:, end_raw:, tag_name:
+      begin_ms = begin_raw.empty? ? 0 : time_to_ms!(begin_raw, tag_name:)
+      end_ms = end_raw.empty? ? nil : time_to_ms!(end_raw, tag_name:)
+
+      if end_ms
+        begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
+        end_ms = begin_ms + 1 if begin_ms == end_ms
+      end
+
+      [begin_ms, end_ms]
+    end
+
+    def merge_section_ranges ranges
+      sorted_ranges = ranges.sort_by { |begin_ms, end_ms| [begin_ms, end_ms || Float::INFINITY] }
+      merged = []
+
+      sorted_ranges.each do |begin_ms, end_ms|
+        if merged.empty?
+          merged << [begin_ms, end_ms]
+          next
+        end
+
+        last_begin_ms, last_end_ms = merged[-1]
+        if last_end_ms.nil? || begin_ms <= last_end_ms
+          merged[-1] = [last_begin_ms, merge_section_end(last_end_ms, end_ms)]
+        else
+          merged << [begin_ms, end_ms]
+        end
+      end
+
+      merged
+    end
+
+    def merge_section_end left_end_ms, right_end_ms
+      return nil if left_end_ms.nil? || right_end_ms.nil?
+
+      [left_end_ms, right_end_ms].max
+    end
+
+    def find_or_create_by_tag_name! locale, name, category:
+      language_code = locale.language_code
+      name = name.to_s.strip
+
+      ApplicationRecord.transaction do
+        tn = TagName.find_or_create_by!(language_code:, name:) do
+          _1.script_code = locale.script_code
+          _1.primary_flg = true
+        end
+
+        tag = tn.tag
+        next tag if tag
+
+        tag = Tag.create!(tag_name_id: tn.id, category:)
+        tn.update!(tag:, primary_flg: true, canonical_id: nil, auto_generated: false)
+        generate_tag_names!(locale, tag, tn)
+        tag.association(:tag_names).reset
+
+        tag
+      end
+    rescue ActiveRecord::RecordNotUnique
+      retry
+    end
+
+    def merge_tags! target_tag, source_tags, created_by_user: nil
+      target_tag => Tag
+
+      affected_post_ids = Set.new
+
+      Tag.transaction do
+        TagVersioning.ensure_snapshot!(target_tag, created_by_user:)
+
+        Array(source_tags).compact.uniq.each do |source_tag|
+          source_tag => Tag
+
+          next if source_tag == target_tag
+
+          TagVersioning.ensure_snapshot!(source_tag, created_by_user:)
+
+          source_tag.post_tags.find_each do |source_pt|
+            post_id = source_pt.post_id
+            affected_post_ids << post_id
+            source_pt.destroy!
+            unless PostTag.exists?(post_id:, tag: target_tag)
+              PostTag.create!(post_id:, tag: target_tag)
+            end
+          end
+
+          source_tag_name = source_tag.tag_name('ja')
+
+          if source_tag_name.wiki_page.present?
+            raise ActiveRecord::RecordInvalid.new(source_tag_name)
+          end
+
+          TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
+          source_tag.tag_names.update_all(tag_id: target_tag.id, primary_flg: false,
+                                          updated_at: Time.current)
+          source_tag.destroy!
+
+          source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
+                                         updated_at: Time.current)
+
+          TagVersioning.record!(target_tag, event_type: :update, created_by_user:)
+        end
+
+        Post.where(id: affected_post_ids.to_a).find_each do |post|
+          PostVersionRecorder.ensure_snapshot!(post, created_by_user:)
+          PostVersionRecorder.record!(post:, event_type: :update, created_by_user:)
+        end
+
+        # 投稿件数を再集計
+        target_tag.update_columns(post_count: PostTag.where(tag: target_tag).count)
+      end
+
+      target_tag.reload
+    end
+
+    def time_to_ms! str, tag_name:
+      match =
+          case str
+          when /\A(?<seconds>\d+)(?:\.(?<ms>\d{1,3}))?\z/
+            { hours: nil, minutes: nil, seconds: Regexp.last_match[:seconds],
+              ms: Regexp.last_match[:ms] }
+          when /\A(?<minutes>\d+):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
+            { hours: nil, minutes: Regexp.last_match[:minutes],
+              seconds: Regexp.last_match[:seconds],
+              ms: Regexp.last_match[:ms] }
+          when /\A(?<hours>\d+):(?<minutes>[0-5]?\d):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
+            { hours: Regexp.last_match[:hours],
+              minutes: Regexp.last_match[:minutes],
+              seconds: Regexp.last_match[:seconds],
+              ms: Regexp.last_match[:ms] }
+          end
+
+      raise SectionLiteralParseError.new(tag_name, str) unless match
+
+      total_s = match[:seconds].to_i
+      total_s += match[:minutes].to_i * 60 if match[:minutes]
+      total_s += match[:hours].to_i * 3_600 if match[:hours]
+
+      total_s * 1_000 + match[:ms].to_s.ljust(3, '0')[0, 3].to_i
+    end
+
+    private
+
+    def generate_tag_names! locale, tag, base_tag_name
+      ApplicationRecord.transaction do
+        locales =
+            Locale
+            .where(deprecated_at: nil)
+            .where.not(language_code: locale.language_code)
+            .order(:language_code, :created_at, :script_code)
+            .uniq { _1.language_code }
+        locales.each do |locale|
+          language_code = locale.language_code
+          script_code = locale.script_code
+          TagName.create!(tag_id: tag.id,
+                          language_code:,
+                          name: TagName.generate_name(locale, tag, base_tag_name),
+                          script_code:,
+                          primary_flg: true,
+                          auto_generated: true,
+                          canonical_id: nil)
+        end
+      end
+    end
   end
 
   private
 
-  def nico_tag_name_must_start_with_nico
-    n = name.to_s
-    if ((nico? && !(n.downcase.start_with?('nico:'))) || 
-        (!(nico?) && n.downcase.start_with?('nico:')))
-      errors.add :name, 'ニコニコ・タグの命名規則に反してゐます．'
-    end
-  end
+  def tag_names_must_be_valid
+    tag_names.each do |tag_name|
+      next if tag_name.valid?
 
-  def tag_name_must_be_canonical
-    if tag_name&.canonical_id?
-      errors.add :tag_name, 'tag_names へは実体を示す必要があります．'
+      tag_name.errors[:name].each { errors.add :name, _1 }
     end
   end
 
@@ -328,36 +389,4 @@ class Tag < ApplicationRecord
       errors.add :category, 'ニジラーと紐づいてゐるタグはニジラー・カテゴリである必要があります．'
     end
   end
-
-  def self.time_to_ms! str, tag_name:
-    match =
-        case str
-        when /\A(?<seconds>\d+)(?:\.(?<ms>\d{1,3}))?\z/
-          { hours: nil, minutes: nil, seconds: Regexp.last_match[:seconds],
-            ms: Regexp.last_match[:ms] }
-        when /\A(?<minutes>\d+):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
-          { hours: nil, minutes: Regexp.last_match[:minutes],
-            seconds: Regexp.last_match[:seconds],
-            ms: Regexp.last_match[:ms] }
-        when /\A(?<hours>\d+):(?<minutes>[0-5]?\d):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
-          { hours: Regexp.last_match[:hours],
-            minutes: Regexp.last_match[:minutes],
-            seconds: Regexp.last_match[:seconds],
-            ms: Regexp.last_match[:ms] }
-        end
-
-    raise SectionLiteralParseError.new(tag_name, str) unless match
-
-    total_s = match[:seconds].to_i
-    total_s += match[:minutes].to_i * 60 if match[:minutes]
-    total_s += match[:hours].to_i * 3_600 if match[:hours]
-
-    total_s * 1_000 + match[:ms].to_s.ljust(3, '0')[0, 3].to_i
-  end
-
-  def nico_tags_cannot_be_deprecated
-    if nico? && deprecated_at.present?
-      errors.add :deprecated_at, 'ニコタグは廃止できません．'
-    end
-  end
 end

backend/app/models/tag_name.rb

@@ -1,45 +1,61 @@
 class TagName < ApplicationRecord
-  include MyDiscard
-
-  has_one :tag
+  belongs_to :language, foreign_key: :language_code, primary_key: :code
+  belongs_to :tag, optional: true
   has_one :wiki_page
 
-  belongs_to :canonical, class_name: 'TagName', optional: true
-  has_many :aliases, class_name: 'TagName', foreign_key: :canonical_id
+  validates :name, presence: true,
+                   length: { maximum: 255 },
+                   uniqueness: { scope: :language_code }
 
-  validates :name, presence: true, length: { maximum: 255 }, uniqueness: true
-
-  validate :canonical_must_be_canonical
   validate :alias_name_must_not_have_prefix
-  validate :canonical_must_not_be_present_with_tag_or_wiki_page
+  validate :alias_must_not_have_wiki_page
   validate :name_must_be_sanitised
+  validate :name_mustnt_start_with_nico
+  validate :generated_name_must_be_reserved
 
-  def self.canonicalise names
+  def primary? = primary_flg
+
+  def self.canonicalise locale, names
     names = Array(names).map { |n| n.to_s.strip }.reject(&:blank?)
     return [] if names.blank?
 
-    tns = TagName.includes(:canonical).where(name: names).index_by(&:name)
+    tns = TagName.where(language_code: locale.language_code, name: names).index_by(&:name)
 
-    names.map { |name| tns[name]&.canonical&.name || name }.uniq
+    names.map { |name|
+      tag_name = tns[name]
+      if !tag_name || tag_name.primary? || tag_name.tag_id.nil?
+        name
+      else
+        TagName.find_by(language_code: locale.language_code,
+                        tag_id: tag_name.tag_id,
+                        primary_flg: true)&.name || name
+      end
+    }.uniq
+  end
+
+  def self.generate_name locale, tag, base_tag_name
+    # TODO: 言語ごとの自動命名ロジック完成したら書く．
+
+    "Tag_##{ tag.id }"
   end
 
   private
 
-  def canonical_must_be_canonical
-    if canonical&.canonical_id?
-      errors.add :canonical, 'canonical は実体を示す必要があります．'
+  def generated_name_must_be_reserved
+    if !auto_generated && name.to_s.start_with?('Tag_#')
+      errors.add :name, 'タグの命名規則に反してゐます．'
     end
   end
 
   def alias_name_must_not_have_prefix
-    if canonical_id? && name.to_s.include?(':')
+    if !(primary?) && name.to_s.include?(':')
       errors.add :name, 'エーリアス名にプレフィクスを含むことはできません．'
     end
   end
 
-  def canonical_must_not_be_present_with_tag_or_wiki_page
-    if canonical_id? && (tag || wiki_page)
-      errors.add :canonical, 'タグもしくは Wiki の参照がある名前はエーリアスになれません．'
+  def alias_must_not_have_wiki_page
+    if !(primary?) && wiki_page
+      errors.add :primary_flg, 'Wiki 参照がある名前はエーリアスになれません．'
     end
   end
 
@@ -48,4 +64,10 @@ class TagName < ApplicationRecord
       errors.add :name, '名前に使用できない文字が含まれてゐます．'
     end
   end
+
+  def name_mustnt_start_with_nico
+    if name.to_s.downcase.start_with?('nico:')
+      errors.add :name, 'タグの命名規則に反してゐます．'
+    end
+  end
 end

backend/app/models/tag_name_sanitisation_rule.rb

@@ -10,35 +10,44 @@ class TagNameSanitisationRule < ApplicationRecord
   validate :source_pattern_must_be_regexp
 
   class << self
-    def sanitise(name) =
-        rules.reduce(name.dup) { |name, (pattern, replacement)| name.gsub(pattern, replacement) }
+    def sanitise(name)
+      rules.reduce(name.dup) { |name, (pattern, replacement)| name.gsub(pattern, replacement) }
+    end
 
     def apply!
-      TagName.find_each do |tn|
-        name = sanitise(tn.name)
-        next if name == tn.name
+      Language.find_each do |language|
+        TagName.where(language:).find_each do |tn|
+          name = sanitise(tn.name)
+          next if name == tn.name
 
-        TagName.transaction do
-          existing_tn = TagName.find_by(name:)
-          if existing_tn
-            existing_tn = existing_tn.canonical || existing_tn
-            next if existing_tn.id == tn.id
+          TagName.transaction do
+            existing_tn = TagName.find_by(language:, name:)
+            if existing_tn
+              unless existing_tn.primary_flg
+                existing_tn = TagName.find_by!(language:,
+                                               tag_id: existing_tn.tag_id,
+                                               primary_flg: true)
+              end
+              next if existing_tn.id == tn.id
 
-            existing_tag = Tag.find_by(tag_name_id: existing_tn.id)
-            source_tag = Tag.find_by(tag_name_id: tn.id)
+              existing_tag = existing_tn.tag
+              source_tag = tn.tag
 
-            if existing_tag
-              Tag.merge_tags!(existing_tag, source_tag) if tn.tag
-            elsif source_tag
-              source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
+              if existing_tag
+                Tag.merge_tags!(existing_tag, source_tag) if tn.tag
+              elsif source_tag
+                tn.update_columns(tag_id: nil, updated_at: Time.current)
+                source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
+                existing_tn.update_columns(tag_id: source_tag.id, updated_at: Time.current)
+              end
+              tn.destroy!
+
+              next
             end
-            tn.discard!
 
-            next
+            # TagName 側の自動サニタイズを回避
+            tn.update_columns(name:, updated_at: Time.current)
           end
-
-          # TagName 側の自動サニタイズを回避
-          tn.update_columns(name:, updated_at: Time.current)
         end
       end
     end

backend/app/models/tag_version.rb

@@ -11,5 +11,6 @@ class TagVersion < ApplicationRecord
                     meta: 'meta' }, validate: true
 
   validates :name, presence: true
+  validates :names, presence: true
   validates :category, presence: true
 end

backend/app/representations/deerjikist_repr.rb

@@ -6,11 +6,12 @@ module DeerjikistRepr
 
   module_function
 
-  def base deerjikist
-    deerjikist.as_json(BASE)
+  def base deerjikist, language_code: 'ja'
+    deerjikist.as_json(BASE).merge(
+        tag: deerjikist.tag && TagRepr.base(deerjikist.tag, language_code:))
   end
 
-  def many deerjikists
-    deerjikists.map { |d| base(d) }
+  def many deerjikists, language_code: 'ja'
+    deerjikists.map { |d| base(d, language_code:) }
   end
 end

backend/app/representations/external_tag_repr.rb

@@ -0,0 +1,20 @@
+module ExternalTagRepr
+  module_function
+
+  def base tag
+    { 'id' => tag.id,
+      'name' => "#{ tag.platform }:#{ tag.name }",
+      'category' => 'nico',
+      'post_count' => tag.post_count,
+      'created_at' => tag.created_at,
+      'updated_at' => tag.created_at,
+      'deprecated_at' => nil,
+      'aliases' => [],
+      'parents' => [],
+      'has_wiki' => false,
+      'material_id' => nil,
+      'has_deerjikists' => false }
+  end
+
+  def inline(tag) = base(tag)
+end

backend/app/representations/material_repr.rb

@@ -12,14 +12,15 @@ module MaterialRepr
 
   module_function
 
-  def base material, host:
+  def base material, host:, language_code: 'ja'
     material.as_json(BASE).merge(
+        tag: material.tag && TagRepr.base(material.tag, language_code:),
         file: if material.file.attached?
                 Rails.application.routes.url_helpers.rails_storage_proxy_url(
                     material.file, host:)
               end,
         thumbnail: thumbnail_url(material, host:),
-        thumbnail_fallback_text: thumbnail_fallback_text(material),
+        thumbnail_fallback_text: thumbnail_fallback_text(material, language_code:),
         thumbnail_fallback_kind: thumbnail_fallback_kind(material),
         media_kind: media_kind(material),
         file_byte_size: material.file_byte_size,
@@ -27,11 +28,11 @@ module MaterialRepr
         export_items: export_items(material))
   end
 
-  def many materials, host:
-    materials.map { |m| base(m, host:) }
+  def many materials, host:, language_code: 'ja'
+    materials.map { |m| base(m, host:, language_code:) }
   end
 
-  def list material, host:
+  def list material, host:, language_code: 'ja'
     { id: material.id,
       version_no: material.version_no,
       url: material.url,
@@ -40,9 +41,9 @@ module MaterialRepr
       source_path: material.source_path,
       source_file_id: material.source_file_id,
       normalized_source_key: material.normalized_source_key,
-      tag: compact_tag(material.tag),
+      tag: compact_tag(material.tag, language_code:),
       thumbnail: thumbnail_url(material, host:),
-      thumbnail_fallback_text: thumbnail_fallback_text(material),
+      thumbnail_fallback_text: thumbnail_fallback_text(material, language_code:),
       thumbnail_fallback_kind: thumbnail_fallback_kind(material),
       media_kind: media_kind(material),
       content_type: material.content_type,
@@ -53,8 +54,8 @@ module MaterialRepr
       export_items: export_items(material) }
   end
 
-  def list_many materials, host:
-    materials.map { |m| list(m, host:) }
+  def list_many materials, host:, language_code: 'ja'
+    materials.map { |m| list(m, host:, language_code:) }
   end
 
   def export_paths material
@@ -79,8 +80,8 @@ module MaterialRepr
         material.thumbnail, host:)
   end
 
-  def thumbnail_fallback_text material
-    material.tag&.name || material.created_at&.strftime('%Y-%m-%d')
+  def thumbnail_fallback_text material, language_code:
+    material.tag&.name(language_code) || material.created_at&.strftime('%Y-%m-%d')
   end
 
   def thumbnail_fallback_kind material
@@ -98,11 +99,11 @@ module MaterialRepr
     'file_other'
   end
 
-  def compact_tag tag
+  def compact_tag tag, language_code:
     return nil unless tag
 
     { id: tag.id,
-      name: tag.name,
+      name: tag.name(language_code),
       category: tag.category,
       deprecated_at: tag.deprecated_at }
   end

backend/app/representations/post_repr.rb

@@ -17,23 +17,23 @@ module PostRepr
 
   module_function
 
-  def base post, current_user = nil, host: nil
+  def base post, current_user = nil, host: nil, language_code: 'ja'
     json =
         if host.present?
           common(post, host:)
         else
           common(post)
         end
-    json['tags'] = tag_json(post)
+    json['tags'] = tag_json(post, language_code:)
     json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
     json['viewed'] = current_user ? current_user.viewed?(post) : false
     json
   end
 
   def detail post, current_user = nil, parent_posts: [], child_posts: [],
-             sibling_posts: { }, related: [], host: nil
+             sibling_posts: { }, related: [], host: nil, language_code: 'ja'
     if host.present?
-      base(post, current_user, host:).merge(
+      base(post, current_user, host:, language_code:).merge(
           'parent_posts' => cards(parent_posts, host:),
           'child_posts' => cards(child_posts, host:),
           'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
@@ -41,7 +41,7 @@ module PostRepr
           },
           'related' => cards(related, host:))
     else
-      base(post, current_user).merge(
+      base(post, current_user, language_code:).merge(
           'parent_posts' => cards(parent_posts),
           'child_posts' => cards(child_posts),
           'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
@@ -86,16 +86,25 @@ module PostRepr
                        end)
   end
 
-  def tag_json post
-    post
-        .active_post_tags
+  def tag_json post, language_code:
+    internal_tags =
+        post
+        .post_tags
         .reject { _1.tag.deprecated? }
-        .sort_by { _1.tag.name }
+        .sort_by { TagRepr.name_for(_1.tag, language_code) }
         .map { |post_tag|
-      TagRepr.inline(post_tag.tag).merge(
-          'children' => [],
-          'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
-    }
+          TagRepr.inline(post_tag.tag, language_code:).merge(
+              'children' => [],
+              'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
+        }
+
+    external_tags =
+        post
+        .external_tags
+        .sort_by { _1.name }
+        .map { ExternalTagRepr.base(_1).merge('children' => [], 'sections' => []) }
+
+    internal_tags + external_tags
   end
 
   def thumbnail_url post, host: nil
@@ -106,11 +115,14 @@ module PostRepr
 
     Rails.application.routes.url_helpers.rails_storage_proxy_url(post.thumbnail, **options)
   rescue ActionController::UrlGenerationError, ArgumentError, URI::InvalidURIError => e
-    Rails.logger.warn(
-        "PostRepr.thumbnail_url failed post_id=#{post.id} " \
-        "attachment_id=#{post.thumbnail.attachment&.id} " \
-        "blob_id=#{post.thumbnail.blob&.id} " \
-        "error_class=#{e.class} message=#{e.message}")
+    payload = {
+        post_id: post.id,
+        attachment_id: post.thumbnail.attachment&.id,
+        blob_id: post.thumbnail.blob&.id,
+        error_class: e.class,
+        message: e.message }
+
+    Rails.logger.warn("PostRepr.thumbnail_url failed #{ payload.to_json }")
     nil
   end
 end

backend/app/representations/tag_repr.rb

@@ -3,18 +3,23 @@
 
 module TagRepr
   BASE = { only: [:id, :category, :post_count, :created_at, :updated_at, :deprecated_at],
-           methods: [:name, :has_wiki, :material_id, :has_deerjikists] }.freeze
+           methods: [:has_wiki, :material_id, :has_deerjikists] }.freeze
 
   module_function
 
-  def base tag
-    tag.as_json(BASE).merge(aliases: tag.snapshot_aliases,
-                            parents: tag.parents.map { _1.as_json(BASE) })
+  def base tag, language_code: 'ja'
+    tag.as_json(BASE).merge(name: name_for(tag, language_code),
+                            aliases: tag.snapshot_aliases(language_code),
+                            parents: tag.parents.map { inline(_1, language_code:) })
   end
 
-  def inline tag
-    tag.as_json(BASE).merge(aliases: [], parents: [])
+  def inline tag, language_code: 'ja'
+    tag.as_json(BASE).merge(name: name_for(tag, language_code), aliases: [], parents: [])
   end
 
-  def many(tags) = tags.map { |t| base(t) }
+  def many(tags, language_code: 'ja') = tags.map { |tag| base(tag, language_code:) }
+
+  def name_for tag, language_code
+    tag.name(language_code) || (tag.system? ? tag.name('ja') : nil)
+  end
 end

backend/app/services/material_version_recorder.rb

@@ -31,7 +31,7 @@ class MaterialVersionRecorder < VersionRecorder
     { url: @record.url,
       parent: @record.parent,
       tag: @record.tag,
-      tag_name: @record.tag&.name,
+      tag_name: @record.tag&.name('ja'),
       tag_category: @record.tag&.category,
       source_kind: @record.source_kind,
       source_uri: @record.source_uri,

backend/app/services/nico_tag_version_recorder.rb

@@ -1,19 +1,22 @@
 class NicoTagVersionRecorder < VersionRecorder
-  def self.record! tag:, event_type:, created_by_user:
-    new(tag:, event_type:, created_by_user:).record!
+  def self.record! external_tag:, event_type:, created_by_user:
+    new(external_tag:, event_type:, created_by_user:).record!
   end
 
-  def initialize tag:, event_type:, created_by_user:
-    super(record: tag, event_type:, created_by_user:)
+  def initialize external_tag:, event_type:, created_by_user:
+    super(record: external_tag, event_type:, created_by_user:)
   end
 
   private
 
   def version_class = NicoTagVersion
   def version_association = :nico_tag_versions
-  def record_key = :tag
+  def record_key = :external_tag
 
   def snapshot_attributes
-    { name: @record.name, linked_tags: @record.snapshot_linked_tag_names.join(' ') }
+    { name: "#{ @record.platform }:#{ @record.name }",
+      linked_tags: @record.snapshot_linked_tag_names.join(' ') }
   end
+
+  def tracks_version_no_on_record? = false
 end

backend/app/services/post_bulk_creator.rb

@@ -6,7 +6,7 @@ class PostBulkCreator
     @host = host
   end
 
-  def run
+  def run locale
     results = Array.new(@posts.length)
     mutex = Mutex.new
     next_index = 0
@@ -27,7 +27,7 @@ class PostBulkCreator
                 break if index >= @posts.length
 
                 attributes = @posts[index]
-                results[index] = create_row(actor, attributes, index)
+                results[index] = create_row(locale, actor, attributes, index)
               rescue StandardError => e
                 Rails.logger.error(
                     "post_bulk_creator_worker_failure #{ { error: e.class.name,
@@ -61,12 +61,12 @@ class PostBulkCreator
 
   private
 
-  def create_row actor, attributes, index
+  def create_row locale, actor, attributes, index
     preflight =
         PostCreatePreflight.new(
             attributes: attributes,
             thumbnail: thumbnail_for(index, attributes),
-            host: @host).run
+            host: @host).run(locale)
     if preflight[:existing_post_id].present?
       return {
           status: 'skipped',
@@ -76,7 +76,7 @@ class PostBulkCreator
 
     post = PostCreator.new(
         actor: actor,
-        attributes: normalised_attributes(attributes, preflight, index)).create!
+        attributes: normalised_attributes(attributes, preflight, index)).create!(locale)
     result = {
         status: 'created',
         post: { id: post.id } }

backend/app/services/post_create_plan.rb

@@ -8,50 +8,50 @@ class PostCreatePlan
     @existing_tags_by_name = nil
   end
 
-  def build!
-    direct_tag_specs, tag_sections = parse_direct_tag_specs
-    default_tag_specs = build_default_tag_specs(direct_tag_specs)
+  def build! locale
+    direct_tag_specs, tag_sections = parse_direct_tag_specs(locale)
+    default_tag_specs = build_default_tag_specs(locale, direct_tag_specs)
     snapshot_tag_specs = merge_tag_specs(direct_tag_specs + default_tag_specs)
-    preload_existing_tags_by_name!(snapshot_tag_specs.map { _1[:name] })
-    validate_new_tag_specs!(snapshot_tag_specs)
-    post_tag_specs = expand_parent_tag_specs(snapshot_tag_specs)
+    preload_existing_tags_by_name!(locale, snapshot_tag_specs.map { _1[:name] })
+    validate_new_tag_specs!(locale, snapshot_tag_specs)
+    post_tag_specs = expand_parent_tag_specs(locale, snapshot_tag_specs)
     video_ms = normalise_video_ms(snapshot_tag_specs)
     validate_video_sections!(video_ms, tag_sections)
     parent_post_ids = normalise_parent_post_ids
     validate_parent_post_ids!(parent_post_ids)
 
-    {
-        url: @attributes[:url],
-        title: @attributes[:title].to_s,
-        thumbnail_base: @attributes[:thumbnail_base].presence,
-        original_created_from: @attributes[:original_created_from].presence,
-        original_created_before: @attributes[:original_created_before].presence,
-        tags: serialised_tags(direct_tag_specs, tag_sections),
-        display_tags: display_tags(direct_tag_specs, tag_sections),
-        duration: @attributes[:duration].to_s,
-        video_ms: video_ms,
-        parent_post_ids: parent_post_ids.join(' '),
-        direct_tag_specs: direct_tag_specs,
-        default_tag_specs: default_tag_specs,
-        snapshot_tag_specs: snapshot_tag_specs,
-        post_tag_specs: post_tag_specs,
-        tag_sections: tag_sections,
-        normalised_parent_post_ids: parent_post_ids }
+    { url: @attributes[:url],
+      title: @attributes[:title].to_s,
+      thumbnail_base: @attributes[:thumbnail_base].presence,
+      original_created_from: @attributes[:original_created_from].presence,
+      original_created_before: @attributes[:original_created_before].presence,
+      tags: serialised_tags(direct_tag_specs, tag_sections),
+      display_tags: display_tags(direct_tag_specs, tag_sections),
+      duration: @attributes[:duration].to_s,
+      video_ms: video_ms,
+      parent_post_ids: parent_post_ids.join(' '),
+      direct_tag_specs: direct_tag_specs,
+      default_tag_specs: default_tag_specs,
+      snapshot_tag_specs: snapshot_tag_specs,
+      post_tag_specs: post_tag_specs,
+      tag_sections: tag_sections,
+      normalised_parent_post_ids: parent_post_ids }
   end
 
   private
 
   def tag_names = @attributes[:tags].to_s.split
 
-  def parse_direct_tag_specs
+  def parse_direct_tag_specs locale
     tag_sections = { }
     direct_tag_specs = []
 
     tag_names.each do |raw_name|
-      tag_name, category, sections = parse_raw_tag_name(raw_name)
-      existing_tag = existing_tags_by_name[tag_name]
-      raise Tag::NicoTagNormalisationError if existing_tag&.nico?
-      raise Tag::DeprecatedTagNormalisationError, [existing_tag.name] if existing_tag&.deprecated?
+      tag_name, category, sections = parse_raw_tag_name(locale, raw_name)
+      existing_tag = existing_tags_by_name(locale)[tag_name]
+      if existing_tag&.deprecated?
+        raise Tag::DeprecatedTagNormalisationError, [existing_tag.name(locale.language_code)]
+      end
 
       direct_tag_specs << {
           name: tag_name,
@@ -67,7 +67,7 @@ class PostCreatePlan
     [merge_tag_specs(direct_tag_specs), tag_sections]
   end
 
-  def parse_raw_tag_name raw_name
+  def parse_raw_tag_name locale, raw_name
     name = raw_name.to_s
     prefix, category =
         Tag::CATEGORY_PREFIXES.find {
@@ -76,7 +76,7 @@ class PostCreatePlan
     name = name.sub(/\A#{ prefix }/i, '')
 
     sections = []
-    while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
+    while match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/)
       name = "#{ match[1] }#{ match[4] }"
       next if match[2].empty? && match[3].empty?
 
@@ -85,19 +85,21 @@ class PostCreatePlan
           end_raw: match[3],
           tag_name: name)
     end
-    raise Tag::SectionLiteralParseError.new(raw_name, raw_name) if name.include?('[') || name.include?(']')
+    if name.include?('[') || name.include?(']')
+      raise Tag::SectionLiteralParseError.new(raw_name, raw_name)
+    end
 
-    [resolved_tag_name(name), category&.to_sym, sections]
+    [resolved_tag_name(locale, name), category&.to_sym, sections]
   end
 
-  def build_default_tag_specs direct_tag_specs
+  def build_default_tag_specs locale, direct_tag_specs
     default_tag_specs = []
     if direct_tag_specs.length < 10 && direct_tag_specs.none? { _1[:name] == TAGME_TAG_NAME }
       default_tag_specs << {
           name: TAGME_TAG_NAME,
           category: :meta }
     end
-    if direct_tag_specs.none? { deerjikist_tag_spec?(_1) }
+    if direct_tag_specs.none? { deerjikist_tag_spec?(locale, _1) }
       default_tag_specs << {
           name: NO_DEERJIKIST_TAG_NAME,
           category: :meta }
@@ -106,17 +108,18 @@ class PostCreatePlan
     default_tag_specs
   end
 
-  def validate_new_tag_specs! specs
+  def validate_new_tag_specs! locale, specs
     Array(specs).each do |spec|
-      next if existing_tags_by_name.key?(spec[:name])
+      next if existing_tags_by_name(locale).key?(spec[:name])
 
-      validate_new_tag_spec!(spec)
+      validate_new_tag_spec!(locale, spec)
     end
   end
 
-  def validate_new_tag_spec! spec
-    tag_name = TagName.new(name: spec[:name])
-    tag = Tag.new(category: spec[:category], tag_name:)
+  def validate_new_tag_spec! locale, spec
+    tag_name = TagName.new(name: spec[:name], language_code: locale.language_code,
+                           script_code: locale.script_code, primary_flg: true)
+    tag = Tag.new(category: spec[:category])
     return if tag_name.valid? && tag.valid?
 
     post = Post.new
@@ -131,20 +134,22 @@ class PostCreatePlan
     raise ActiveRecord::RecordInvalid, post
   end
 
-  def expand_parent_tag_specs snapshot_tag_specs
-    existing_snapshot_tags = snapshot_tag_specs.filter_map { existing_tags_by_name[_1[:name]] }
+  def expand_parent_tag_specs locale, snapshot_tag_specs
+    existing_snapshot_tags = snapshot_tag_specs.filter_map do
+      existing_tags_by_name(locale)[_1[:name]]
+    end
     expanded_parent_specs =
         Tag.expand_parent_tags(existing_snapshot_tags)
            .reject(&:deprecated?)
            .map { |tag|
-             {
-                 name: tag.name,
-                 category: tag.category.to_sym } }
+             { name: tag.name(locale.language_code),
+               category: tag.category.to_sym }
+        }
     merge_tag_specs(snapshot_tag_specs + expanded_parent_specs)
   end
 
   def merge_tag_specs specs
-    specs.each_with_object({ }) do |spec, merged|
+    specs.each_with_object({ }) { |spec, merged|
       merged[spec[:name]] =
           if merged.key?(spec[:name]) && merged[spec[:name]][:category] != :general
             merged[spec[:name]]
@@ -153,36 +158,40 @@ class PostCreatePlan
                 name: spec[:name],
                 category: spec[:category] }
           end
-    end.values.sort_by { _1[:name] }
+    }.values.sort_by { _1[:name] }
   end
 
-  def existing_tags_by_name
+  def existing_tags_by_name locale
     @existing_tags_by_name ||= begin
-      names = tag_names.map { canonical_tag_name_without_sections(_1) }.uniq
-      Tag.joins(:tag_name).where(tag_names: { name: names }).index_by(&:name)
+      names = tag_names.map { canonical_tag_name_without_sections(locale, _1) }.uniq
+      TagName.where(language_code: locale.language_code, primary_flg: true, name: names)
+             .includes(:tag)
+             .each_with_object({ }) { |tag_name, tags| tags[tag_name.name] = tag_name.tag }
     end
   end
 
-  def preload_existing_tags_by_name! names
+  def preload_existing_tags_by_name! locale, names
     wanted_names = Array(names).map { _1.to_s }.reject(&:blank?).uniq
-    missing_names = wanted_names - existing_tags_by_name.keys
+    missing_names = wanted_names - existing_tags_by_name(locale).keys
     return if missing_names.empty?
 
-    existing_tags_by_name.merge!(
-        Tag.joins(:tag_name)
-           .where(tag_names: { name: missing_names })
-           .index_by(&:name))
+    existing_tags_by_name(locale).merge!(
+        TagName.where(language_code: locale.language_code,
+                      primary_flg: true,
+                      name: missing_names)
+               .includes(:tag)
+               .each_with_object({ }) { |tag_name, tags| tags[tag_name.name] = tag_name.tag })
   end
 
-  def canonical_tag_name_without_sections raw_name
-    name, = parse_raw_tag_name(raw_name)
+  def canonical_tag_name_without_sections locale, raw_name
+    name, = parse_raw_tag_name(locale, raw_name)
     name
   end
 
-  def deerjikist_tag_spec? spec
+  def deerjikist_tag_spec? locale, spec
     return true if spec[:category] == :deerjikist
 
-    existing_tags_by_name[spec[:name]]&.deerjikist?
+    existing_tags_by_name(locale)[spec[:name]]&.deerjikist?
   end
 
   def normalise_parent_post_ids
@@ -260,10 +269,12 @@ class PostCreatePlan
     end
   end
 
-  def resolved_tag_name name
-    tag_name = TagName.includes(:canonical).find_by(name:)
-    return name if tag_name.nil?
+  def resolved_tag_name locale, name
+    tag_name = TagName.find_by(language_code: locale.language_code, name:)
+    return name if !(tag_name) || tag_name.primary?
 
-    (tag_name.canonical || tag_name).name
+    TagName.find_by(language_code: locale.language_code,
+                    tag_id: tag_name.tag_id,
+                    primary_flg: true)&.name || name
   end
 end

backend/app/services/post_create_preflight.rb

@@ -15,9 +15,10 @@ class PostCreatePreflight
     @host = host
   end
 
-  def run
+  def run locale
     preview = PostImportPreviewer.new.preview_rows(
         rows: [preview_row],
+        locale:,
         fetch_metadata: false).first
     if preview[:existing_post_id].present?
       return {
@@ -53,7 +54,7 @@ class PostCreatePreflight
             original_created_from: preview[:attributes]['original_created_from'],
             original_created_before: preview[:attributes]['original_created_before'],
             duration: preview[:attributes]['duration'],
-            video_ms: preview[:attributes]['video_ms'] }).build!
+            video_ms: preview[:attributes]['video_ms'] }).build!(locale)
 
     {
         url: plan[:url],

backend/app/services/post_creator.rb

@@ -9,7 +9,7 @@ class PostCreator
     @field_warnings = { }
   end
 
-  def create!
+  def create! locale
     thumbnail_attachment = prepare_thumbnail_attachment
     post = Post.new(title: @attributes[:title].presence,
                     url: @attributes[:url],
@@ -21,14 +21,17 @@ class PostCreator
     ApplicationRecord.transaction do
       post.save!
       post.thumbnail.attach(thumbnail_attachment) if thumbnail_attachment.present?
-      snapshot_tags = planned_snapshot_tags
-      post_tags = planned_post_tags
-      sections = planned_sections
-      TagVersioning.record_tag_snapshots!(snapshot_tags, created_by_user: @actor)
-      post.video_ms = planned_video_ms
+      snapshot_tags = planned_snapshot_tags(locale)
+      post_tags = planned_post_tags(locale)
+      sections = planned_sections(locale)
+      TagVersioning.record_tag_snapshots!(
+          snapshot_tags,
+          created_by_user: @actor,
+          language_code: locale.language_code)
+      post.video_ms = planned_video_ms(locale)
       post.save!
       sync_post_tags!(post, post_tags, sections)
-      sync_parent_posts!(post, planned_parent_post_ids)
+      sync_parent_posts!(post, planned_parent_post_ids(locale))
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: @actor)
     end
     post
@@ -45,69 +48,73 @@ class PostCreator
         thumbnail_base: @attributes[:thumbnail_base].presence)
   end
 
-  def planned_snapshot_tags = planned_create_attributes[:snapshot_tags]
+  def planned_snapshot_tags(locale) = planned_create_attributes(locale)[:snapshot_tags]
 
-  def planned_post_tags = planned_create_attributes[:post_tags]
+  def planned_post_tags(locale) = planned_create_attributes(locale)[:post_tags]
 
-  def planned_sections = planned_create_attributes[:tag_sections]
+  def planned_sections(locale) = planned_create_attributes(locale)[:tag_sections]
 
-  def planned_parent_post_ids = planned_create_attributes[:normalised_parent_post_ids]
-
-  def planned_video_ms
-    planned_create_attributes[:video_ms]
+  def planned_parent_post_ids locale
+    planned_create_attributes(locale)[:normalised_parent_post_ids]
   end
 
-  def planned_create_attributes
+  def planned_video_ms locale
+    planned_create_attributes(locale)[:video_ms]
+  end
+
+  def planned_create_attributes locale
     @planned_create_attributes ||= begin
       if @attributes.key?(:snapshot_tag_specs)
-        snapshot_tags = materialise_tags(@attributes[:snapshot_tag_specs] || [])
-        post_tags = materialise_tags(@attributes[:post_tag_specs] || [])
+        snapshot_tags = materialise_tags(locale, @attributes[:snapshot_tag_specs] || [])
+        post_tags = materialise_tags(locale, @attributes[:post_tag_specs] || [])
         {
             snapshot_tags: snapshot_tags,
             post_tags: post_tags,
             tag_sections: materialise_sections(
                 @attributes[:tag_sections] || { },
                 snapshot_tags,
-                post_tags),
+                post_tags,
+                locale),
             normalised_parent_post_ids: @attributes[:normalised_parent_post_ids] || [],
             video_ms: @attributes[:video_ms] }
       else
-        build_materialised_plan
+        build_materialised_plan(locale)
       end
     end
   end
 
-  def build_materialised_plan
-    plan = PostCreatePlan.new(attributes: @attributes).build!
-    snapshot_tags = materialise_tags(plan[:snapshot_tag_specs] || [])
-    post_tags = materialise_tags(plan[:post_tag_specs] || [])
+  def build_materialised_plan locale
+    plan = PostCreatePlan.new(attributes: @attributes).build!(locale)
+    snapshot_tags = materialise_tags(locale, plan[:snapshot_tag_specs] || [])
+    post_tags = materialise_tags(locale, plan[:post_tag_specs] || [])
     {
         snapshot_tags: snapshot_tags,
         post_tags: post_tags,
         tag_sections: materialise_sections(
             plan[:tag_sections] || { },
             snapshot_tags,
-            post_tags),
+            post_tags,
+            locale),
         normalised_parent_post_ids: plan[:normalised_parent_post_ids] || [],
         video_ms: plan[:video_ms] }
   end
 
-  def materialise_tags specs
+  def materialise_tags locale, specs
     Array(specs).each_with_object({ }) do |spec, tags|
       name = spec[:name] || spec['name']
       category = spec[:category] || spec['category']
       next if name.blank? || category.blank?
 
-      tag = Tag.find_or_create_by_tag_name!(name, category:)
+      tag = Tag.find_or_create_by_tag_name!(locale, name, category:)
       tag.update!(category:) if tag.category.to_sym != category.to_sym
       tags[name] ||= tag
     end.values
   end
 
-  def materialise_sections sections_by_name, snapshot_tags, post_tags
-    tags_by_name = post_tags.index_by(&:name)
+  def materialise_sections sections_by_name, snapshot_tags, post_tags, locale = Locale.nipponese
+    tags_by_name = post_tags.index_by { _1.name(locale.language_code) }
     snapshot_tags.each do |tag|
-      tags_by_name[tag.name] ||= tag
+      tags_by_name[tag.name(locale.language_code)] ||= tag
     end
 
     sections_by_name.each_with_object({ }) do |(tag_name, ranges), sections|
@@ -121,9 +128,11 @@ class PostCreator
   def sync_post_tags! post, desired_tags, sections
     desired_ids = desired_tags.map(&:id).to_set
     current_ids = post.tags.pluck(:id).to_set
+
     Tag.where(id: desired_ids - current_ids).find_each do |tag|
       PostTag.create_or_find_by!(post:, tag:, created_user: @actor)
     end
+
     PostTagSection.where(post_id: post.id).destroy_all
     sections.each do |tag_id, ranges|
       ranges.each do |begin_ms, end_ms|
@@ -133,10 +142,9 @@ class PostCreator
                                end_ms:)
       end
     end
+
     PostTag.where(post_id: post.id,
-                  tag_id: (current_ids - desired_ids).to_a).kept.find_each do |post_tag|
-      post_tag.discard_by!(@actor)
-    end
+                  tag_id: (current_ids - desired_ids).to_a).destroy_all
   end
 
   def sync_parent_posts! post, ids

backend/app/services/post_import_previewer.rb

@@ -16,7 +16,7 @@ class PostImportPreviewer
   THUMBNAIL_FETCH_WARNING = 'サムネールを取得できませんでした．'.freeze
   METADATA_FETCH_WARNING = '自動取得に失敗しました．'.freeze
 
-  def preview_rows rows:, fetch_metadata: true, metadata_cache: { }
+  def preview_rows rows:, locale: Locale.nipponese, fetch_metadata: true, metadata_cache: { }
     prepared_rows = rows.map { prepare_row(_1) }
     url_counts = prepared_rows.filter_map { _1[:normal_url] }.tally
     existing_posts =
@@ -30,13 +30,14 @@ class PostImportPreviewer
         url_counts)
     known_tags =
         preload_known_tags(
+            locale,
             prepared_rows,
             fetch_metadata,
             metadata_cache,
             existing_posts,
             url_counts)
     prepared_rows.map { |row|
-      preview_row(row,
+      preview_row(locale, row,
                   fetch_metadata:,
                   metadata_cache:,
                   existing_posts:,
@@ -59,7 +60,7 @@ class PostImportPreviewer
     source.merge(url_text: url, normal_url:, url_error: validate_url_safety(normal_url))
   end
 
-  def preview_row row,
+  def preview_row locale, row,
                   fetch_metadata:,
                   metadata_cache:,
                   existing_posts:,
@@ -124,7 +125,8 @@ class PostImportPreviewer
 
     attributes['url'] = url
     validate_basic_data(attributes, validation_errors)
-    validate_preview_tags(merged_tags(tag_sources, provenance['tags']),
+    validate_preview_tags(locale,
+                          merged_tags(tag_sources, provenance['tags']),
                           validation_errors,
                           known_tags)
     validate_parents(attributes['parent_post_ids'], validation_errors, existing_parent_ids)
@@ -225,15 +227,15 @@ class PostImportPreviewer
     end
     { data:, warnings:, validation_errors: { } }
   rescue Preview::UrlSafety::UnsafeUrl => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.info(
-        "post_import_metadata_fetch_unsafe_url "\
-        "#{ { error: e.class.name, message: e.message }.to_json }")
+        "post_import_metadata_fetch_unsafe_url #{ payload.to_json }")
     { data: { }, warnings: { }, validation_errors: { url: [e.message] } }
   rescue Preview::HttpFetcher::FetchFailed,
          Preview::HttpFetcher::ResponseTooLarge => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.info(
-        "post_import_metadata_fetch_failure "\
-        "#{ { error: e.class.name, message: e.message }.to_json }")
+        "post_import_metadata_fetch_failure #{ payload.to_json }")
     { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
   end
 
@@ -335,18 +337,18 @@ class PostImportPreviewer
   def safe_fetch_metadata url
     fetch_metadata(url)
   rescue Preview::UrlSafety::UnsafeUrl => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.info(
-        "post_import_metadata_fetch_unsafe_url "\
-        "#{ { error: e.class.name, message: e.message }.to_json }")
+        "post_import_metadata_fetch_unsafe_url #{ payload.to_json }")
     { data: { }, warnings: { }, validation_errors: { url: [e.message] } }
   rescue StandardError => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.error(
-        "post_import_metadata_fetch_unexpected_failure "\
-        "#{ { error: e.class.name, message: e.message }.to_json }")
+        "post_import_metadata_fetch_unexpected_failure #{ payload.to_json }")
     { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
   end
 
-  def preload_known_tags prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
+  def preload_known_tags locale, prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
     names = prepared_rows.flat_map { |row|
       attributes = initial_attributes(row)
       provenance = initial_provenance(row)
@@ -358,15 +360,13 @@ class PostImportPreviewer
         metadata = metadata_for(row[:normal_url], metadata_cache)
         apply_metadata!(attributes, provenance, tag_sources, metadata[:data])
       end
-      preview_tag_names(merged_tags(tag_sources, provenance['tags']))
+      preview_tag_names(locale, merged_tags(tag_sources, provenance['tags']))
     }.compact.uniq
     return { } if names.empty?
 
-    Tag.joins(:tag_name)
-      .where(tag_names: { name: names })
-      .includes(:tag_name)
-      .to_a
-      .index_by(&:name)
+    TagName.where(language_code: locale.language_code, primary_flg: true, name: names)
+           .includes(:tag)
+           .each_with_object({ }) { |tag_name, tags| tags[tag_name.name] = tag_name.tag }
   end
 
   def preload_parent_ids prepared_rows
@@ -437,19 +437,21 @@ class PostImportPreviewer
     sources['automatic'].to_s
   end
 
-  def preview_tag_names raw
+  def preview_tag_names locale, raw
     names = raw.to_s.split
     return [] if names.empty?
     if names.any? { _1.downcase.start_with?('nico:') }
       return []
     end
 
-    names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
+    names.map { |name|
+      TagName.canonicalise(locale, name.sub(/\[.*\]\z/, '')).first
+    }
   rescue Tag::SectionLiteralParseError
     []
   end
 
-  def validate_preview_tags raw, errors, known_tags
+  def validate_preview_tags locale, raw, errors, known_tags
     names = raw.to_s.split
     return if names.empty?
     if names.any? { _1.downcase.start_with?('nico:') }
@@ -457,9 +459,11 @@ class PostImportPreviewer
       return
     end
 
-    parsed = names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
+    parsed = names.map { |name|
+      TagName.canonicalise(locale, name.sub(/\[.*\]\z/, '')).first
+    }
     existing = parsed.filter_map { known_tags[_1] }
-    deprecated = existing.select(&:deprecated?).map(&:name)
+    deprecated = existing.select(&:deprecated?).map { _1.name(locale.language_code) }
     errors[:tags] = ["廃止済みタグがあります: #{ deprecated.join(' ') }"] if deprecated.present?
   rescue Tag::SectionLiteralParseError
     errors[:tags] = ['タグ区間の記法が不正です．']

backend/app/services/post_metadata_fetcher.rb

@@ -3,10 +3,9 @@ require 'date'
 
 class PostMetadataFetcher
   TIMESTAMP_PATTERN =
-      Regexp.new(
-          '\A(\d{4})-(\d{2})-(\d{2})T(\d{2})' \
-          '(?::(\d{2})(?::(\d{2})(?:\.(\d+))?)?)?' \
-          '(Z|[+-]\d{2}:?\d{2})?\z')
+      /\A(\d{4})-(\d{2})-(\d{2})T(\d{2})
+        (?::(\d{2})(?::(\d{2})(?:\.(\d+))?)?)?
+        (Z|[+-]\d{2}:?\d{2})?\z/x
 
   def self.fetch raw_url
     uri, = Preview::UrlSafety.validate(raw_url)
@@ -48,9 +47,9 @@ class PostMetadataFetcher
 
     existing_tags =
         Tag
-        .joins(:tag_name)
-        .where(tag_names: { name: names })
-        .index_by(&:name)
+        .joins(:tag_names)
+        .where(tag_names: { language_code: 'ja', primary_flg: true, name: names })
+        .index_by { _1.name('ja') }
 
     names.map { |name|
       tag = existing_tags[name]

backend/app/services/post_version_recorder.rb

@@ -25,6 +25,7 @@ class PostVersionRecorder < VersionRecorder
       thumbnail_base: @record.thumbnail_base,
       video_ms: @record.video_ms,
       tags: @record.snapshot_tag_names.join(' '),
+      tags_json: @record.snapshot_tags_json,
       parent_post_ids: @record.snapshot_parent_post_ids.join(' '),
       original_created_from: @record.original_created_from,
       original_created_before: @record.original_created_before }

backend/app/services/tag_version_recorder.rb

@@ -1,5 +1,5 @@
 class TagVersionRecorder < VersionRecorder
-  def self.record! tag:, event_type:, created_by_user:
+  def self.record! tag:, event_type:, created_by_user:, **_options
     new(tag:, event_type:, created_by_user:).record!
   end
 
@@ -14,10 +14,29 @@ class TagVersionRecorder < VersionRecorder
   def record_key = :tag
 
   def snapshot_attributes
-    { name: @record.name,
+    names = snapshot_names
+    compatibility_names = names.fetch('ja')
+
+    { name: compatibility_names.fetch('name'),
       category: @record.category,
       deprecated_at: @record.deprecated_at,
-      aliases: @record.snapshot_aliases.join(' '),
+      aliases: compatibility_names.fetch('aliases').map { _1.fetch('name') }.join(' '),
+      names:,
       parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
   end
+
+  def snapshot_names
+    @record.tag_names.order(:language_code, :name).group_by(&:language_code)
+        .transform_values do |tag_names|
+      primary = tag_names.find(&:primary?)
+      aliases = tag_names.reject(&:primary?).sort_by(&:name).map { |tag_name|
+        { 'name' => tag_name.name, 'script_code' => tag_name.script_code }
+      }
+
+      { 'name' => primary.name,
+        'script_code' => primary.script_code,
+        'auto_generated' => primary.auto_generated,
+        'aliases' => aliases }
+    end
+  end
 end

backend/app/services/tag_versioning.rb

@@ -1,38 +1,22 @@
 class TagVersioning
-  def self.record! tag, event_type:, created_by_user:
-    if tag.nico?
-      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
-    else
-      TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
-    end
+  def self.record! tag, event_type:, created_by_user:, language_code: 'ja'
+    TagVersionRecorder.record!(tag:, event_type:, created_by_user:, language_code:)
   end
 
-  def self.ensure_snapshot! tag, created_by_user:
-    if tag.nico?
-      return if tag.nico_tag_versions.exists?
+  def self.ensure_snapshot! tag, created_by_user:, language_code: 'ja'
+    return if tag.tag_versions.exists?
 
-      NicoTagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
-    else
-      return if tag.tag_versions.exists?
-
-      TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
-    end
+    TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:, language_code:)
   end
 
-  def self.record_tag_snapshot! tag, created_by_user:
-    event_type =
-        if tag.nico?
-          tag.nico_tag_versions.exists? ? :update : :create
-        else
-          tag.tag_versions.exists? ? :update : :create
-        end
-
-    record!(tag, event_type:, created_by_user:)
+  def self.record_tag_snapshot! tag, created_by_user:, language_code: 'ja'
+    event_type = tag.tag_versions.exists? ? :update : :create
+    record!(tag, event_type:, created_by_user:, language_code:)
   end
 
-  def self.record_tag_snapshots! tags, created_by_user:
+  def self.record_tag_snapshots! tags, created_by_user:, language_code: 'ja'
     tags.each do |tag|
-      record_tag_snapshot!(tag, created_by_user:)
+      record_tag_snapshot!(tag, created_by_user:, language_code:)
     end
   end
 end

backend/app/services/theatre_post_selector.rb

@@ -41,7 +41,7 @@ class TheatrePostSelector
   def weighted_candidates
     @weighted_candidates ||= begin
       penalties = tag_penalties
-      posts = eligible_posts.includes(tags: :tag_name).to_a
+      posts = eligible_posts.includes(tags: :tag_names).to_a
 
       posts.map do |post|
         post_tags = post.tags.to_a
@@ -82,7 +82,7 @@ class TheatrePostSelector
   def tag_penalty_json
     return [] if tag_penalties.empty?
 
-    tags = Tag.where(id: tag_penalties.keys).includes(:tag_name).index_by(&:id)
+    tags = Tag.where(id: tag_penalties.keys).includes(:tag_names).index_by(&:id)
 
     tag_penalties
       .map { |tag_id, penalty|
@@ -113,7 +113,7 @@ class TheatrePostSelector
 
   def light_tag_json tag
     { id: tag.id,
-      name: tag.name,
+      name: tag.name('ja'),
       category: tag.category }
   end
 end

backend/app/services/version_recorder.rb

@@ -47,10 +47,14 @@ class VersionRecorder
   end
 
   def update_record_version_no! version_no
+    return unless tracks_version_no_on_record?
+
     @record.update_columns(version_no:)
     @record.version_no = version_no
   end
 
+  def tracks_version_no_on_record? = true
+
   def validate_version_sequence! latest
     if !(latest) && @event_type != 'create'
       raise "#{ version_class.name } first event must be create"
@@ -60,7 +64,7 @@ class VersionRecorder
       raise "#{ version_class.name } create event already exists"
     end
 
-    return unless latest
+    return if !(latest) || !(tracks_version_no_on_record?)
 
     if @record.version_no != latest.version_no
       raise ("#{ record_class.name }##{ @record.id } version_no is #{ @record.version_no }, " +

backend/app/services/youtube/sync.rb

@@ -103,7 +103,7 @@ module Youtube
     end
 
     def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
-      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      current_tag_ids ||= PostTag.where(post_id: post.id).pluck(:tag_id).to_set
       desired_tag_ids = desired_tag_ids.compact.to_set
 
       to_add = desired_tag_ids - current_tag_ids
@@ -117,8 +117,8 @@ module Youtube
         end
       end
 
-      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
-        pt.discard_by!(nil)
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each do |pt|
+        pt.destroy!
       end
     end
 

backend/config/environments/development.rb

@@ -1,4 +1,4 @@
-require "active_support/core_ext/integer/time"
+require 'active_support/core_ext/integer/time'
 
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
@@ -17,8 +17,8 @@ Rails.application.configure do
 
   # Enable/disable Action Controller caching. By default Action Controller caching is disabled.
   # Run rails dev:cache to toggle Action Controller caching.
-  if Rails.root.join("tmp/caching-dev.txt").exist?
-    config.public_file_server.headers = { "cache-control" => "public, max-age=#{2.days.to_i}" }
+  if Rails.root.join('tmp/caching-dev.txt').exist?
+    config.public_file_server.headers = { 'cache-control' => "public, max-age=#{2.days.to_i}" }
   else
     config.action_controller.perform_caching = false
   end

backend/config/routes.rb

@@ -1,5 +1,5 @@
 Rails.application.routes.draw do
-  resources :nico_tags, path: 'tags/nico', only: [:index, :update]
+  resources :nico_tags, path: 'tags/nico', only: [:index, :show, :update]
 
   scope 'tags/:parent_id/children', controller: :tag_children do
     post ':child_id', action: :create
@@ -55,7 +55,6 @@ Rails.application.routes.draw do
       get :metadata
       post :bulk
       get :random
-      get :changes
       get :versions, to: 'post_versions#index'
     end
 

backend/db/migrate/20260727123600_add_tags_json_to_post_versions.rb

@@ -0,0 +1,299 @@
+class AddTagsJsonToPostVersions < ActiveRecord::Migration[8.0]
+  RESOLUTION_GRACE = 1.second
+  SECTION_LITERAL_PATTERN = /\[[^\[\]\s]*-[^\[\]\s]*\]\z/
+
+  class MigrationPostVersion < ActiveRecord::Base
+    self.table_name = 'post_versions'
+  end
+
+  class MigrationTag < ActiveRecord::Base
+    self.table_name = 'tags'
+  end
+
+  class MigrationTagName < ActiveRecord::Base
+    self.table_name = 'tag_names'
+  end
+
+  class MigrationTagVersion < ActiveRecord::Base
+    self.table_name = 'tag_versions'
+  end
+
+  class MigrationNicoTagVersion < ActiveRecord::Base
+    self.table_name = 'nico_tag_versions'
+  end
+
+  def up
+    add_column :post_versions, :tags_json, :json, after: :tags
+    MigrationPostVersion.reset_column_information
+
+    backfill_missing_initial_tag_versions!
+    intervals_by_name = build_intervals_by_name
+
+    say_with_time 'Backfilling post_versions.tags_json' do
+      MigrationPostVersion.where(tags_json: nil).find_each(batch_size: 500) do |version|
+        version.update_columns(tags_json: build_tags_json(version, intervals_by_name))
+      end
+    end
+
+    change_column_null :post_versions, :tags_json, false
+
+    schema = connection.quote(JSON.generate({
+        type: 'array',
+        items: { type: 'object',
+                 properties: { id: { type: 'integer', minimum: 1 },
+                               version_no: { type: 'integer', minimum: 1 },
+                               name: { type: 'string', minLength: 1 },
+                               category: { type: 'string', enum: ['deerjikist',
+                                                                  'meme',
+                                                                  'character',
+                                                                  'general',
+                                                                  'material',
+                                                                  'meta',
+                                                                  'nico'] },
+                               sections: { type: 'array',
+                                           items: { type: 'object',
+                                                    properties: { begin_ms: { type: 'integer',
+                                                                              minimum: 0 },
+                                                                  end_ms: { type: ['integer',
+                                                                                   'null'],
+                                                                            minimum: 0 } },
+                                                    required: ['begin_ms', 'end_ms'],
+                                                    additionalProperties: false } } },
+                 required: ['id', 'version_no', 'name', 'category', 'sections'],
+                 additionalProperties: false } }))
+
+    add_check_constraint :post_versions,
+                         "JSON_SCHEMA_VALID(#{ schema }, tags_json)",
+                         name: 'chk_post_versions_tags_json_schema'
+  end
+
+  def down
+    remove_check_constraint :post_versions, name: 'chk_post_versions_tags_json_schema'
+
+    remove_column :post_versions, :tags_json
+  end
+
+  private
+
+  def backfill_missing_initial_tag_versions!
+    say_with_time 'Backfilling missing initial tag versions' do
+      tag_rows = missing_initial_version_rows(MigrationTagVersion, nico: false)
+      nico_rows = missing_initial_version_rows(MigrationNicoTagVersion, nico: true)
+
+      MigrationTagVersion.insert_all!(tag_rows) if tag_rows.any?
+      MigrationNicoTagVersion.insert_all!(nico_rows) if nico_rows.any?
+
+      tag_rows.length + nico_rows.length
+    end
+  end
+
+  def missing_initial_version_rows version_class, nico:
+    first_versions =
+        version_class
+        .order(:tag_id, :version_no)
+        .to_a
+        .group_by(&:tag_id)
+        .transform_values(&:first)
+    rows = []
+
+    MigrationTag.find_each do |tag|
+      next if (tag.category == 'nico') != nico
+
+      first_version = first_versions[tag.id]
+      next unless first_version
+      next if valid_initial_version?(first_version)
+
+      assert_inferable_initial_version!(tag, first_version)
+      rows << initial_version_row(tag, first_version, nico:)
+    end
+
+    rows
+  end
+
+  def valid_initial_version? version
+    version.version_no == 1 && version.event_type == 'create'
+  end
+
+  def assert_inferable_initial_version! tag, version
+    inferable =
+        version.version_no == 2 &&
+        version.event_type == 'discard' &&
+        tag.created_at < version.created_at
+    return if inferable
+
+    details = [
+        "tag_id=#{ tag.id }",
+        "version_no=#{ version.version_no }",
+        "event_type=#{ version.event_type.inspect }",
+        "tag_created_at=#{ tag.created_at.iso8601(6) }",
+        "version_created_at=#{ version.created_at.iso8601(6) }"]
+
+    raise "Cannot infer initial tag version: #{ details.join(', ') }"
+  end
+
+  def initial_version_row tag, discard_version, nico:
+    row = {
+        tag_id: tag.id,
+        version_no: 1,
+        event_type: 'create',
+        name: discard_version.name,
+        created_at: tag.created_at,
+        created_by_user_id: nil }
+
+    if nico
+      return row.merge(linked_tags: discard_version.linked_tags)
+    end
+
+    row.merge(
+        category: discard_version.category,
+        aliases: discard_version.aliases,
+        parent_tag_ids: discard_version.parent_tag_ids,
+        deprecated_at: discard_version.deprecated_at)
+  end
+
+  def build_intervals_by_name
+    intervals_by_name = Hash.new { |hash, name| hash[name] = [] }
+    versions_by_kind = {
+        tag: versions_by_tag_id(MigrationTagVersion),
+        nico: versions_by_tag_id(MigrationNicoTagVersion) }
+    current_names = current_names_by_tag_id
+
+    MigrationTag.find_each do |tag|
+      nico = tag.category == 'nico'
+      kind = nico ? :nico : :tag
+      versions = versions_by_kind.fetch(kind).fetch(tag.id, [])
+
+      intervals_for(
+          tag,
+          versions,
+          current_name: current_names.fetch(tag.id),
+          nico:).each do |interval|
+        name = interval.delete(:name)
+        intervals_by_name[name] << interval
+      end
+    end
+
+    intervals_by_name
+  end
+
+  def versions_by_tag_id version_class
+    version_class
+        .order(:tag_id, :version_no)
+        .to_a
+        .group_by(&:tag_id)
+  end
+
+  def current_names_by_tag_id
+    MigrationTagName
+        .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.id')
+        .pluck('tags.id', 'tag_names.name')
+        .to_h
+  end
+
+  def intervals_for tag, versions, current_name:, nico:
+    if versions.empty?
+      return [{
+          name: current_name,
+          tag_id: tag.id,
+          version_no: tag.version_no,
+          category: nico ? 'nico' : tag.category,
+          from: tag.created_at,
+          to: tag.discarded_at }]
+    end
+
+    versions.each_with_index.filter_map do |version, index|
+      next if version.event_type == 'discard'
+
+      {
+          name: version.name,
+          tag_id: tag.id,
+          version_no: version.version_no,
+          category: nico ? 'nico' : version.category,
+          from: version.created_at,
+          to: versions[index + 1]&.created_at || tag.discarded_at }
+    end
+  end
+
+  def build_tags_json version, intervals_by_name
+    entries = version.tags.to_s.split.map do |literal|
+      name = tag_name_from_literal(literal)
+      interval = resolve_tag!(intervals_by_name.fetch(name, []), name:, version:)
+
+      { 'id' => interval.fetch(:tag_id),
+        'version_no' => interval.fetch(:version_no),
+        'name' => name,
+        'category' => interval.fetch(:category),
+        'sections' => [] }
+    end
+
+    assert_unique_tag_ids!(version, entries)
+
+    entries.sort_by { |entry| entry.fetch('id') }
+  end
+
+  def tag_name_from_literal literal
+    name = literal.dup
+    name.sub!(SECTION_LITERAL_PATTERN, '') while name.match?(
+        SECTION_LITERAL_PATTERN)
+
+    if name.empty? || name.include?('[') || name.include?(']')
+      raise "Invalid legacy tag literal: #{ literal.inspect }"
+    end
+
+    name
+  end
+
+  def resolve_tag! intervals, name:, version:
+    time = version.created_at
+    candidates = intervals.select do |interval|
+      interval.fetch(:from) <= time &&
+        (interval[:to].nil? || time < interval.fetch(:to))
+    end
+
+    candidates = future_candidates(intervals, time) if candidates.empty?
+
+    return candidates.first if candidates.one?
+
+    candidate_versions = candidates.map do |candidate|
+      [candidate.fetch(:tag_id), candidate.fetch(:version_no)]
+    end
+    details = [
+        "post_version_id=#{ version.id }",
+        "post_id=#{ version.post_id }",
+        "name=#{ name.inspect }",
+        "created_at=#{ time.iso8601(6) }",
+        "candidates=#{ candidate_versions.inspect }"].join(', ')
+
+    raise "Could not resolve tag snapshot: #{ details }"
+  end
+
+  def future_candidates intervals, time
+    candidates = intervals.select do |interval|
+      interval.fetch(:from) > time &&
+        interval.fetch(:from) <= time + RESOLUTION_GRACE
+    end
+    return [] if candidates.empty?
+
+    nearest_from = candidates.map { |interval| interval.fetch(:from) }.min
+
+    candidates.select do |interval|
+      interval.fetch(:from) == nearest_from
+    end
+  end
+
+  def assert_unique_tag_ids! version, entries
+    duplicate_tag_ids =
+        entries
+        .map { |entry| entry.fetch('id') }
+        .tally
+        .select { |_tag_id, count| count > 1 }
+        .keys
+    return if duplicate_tag_ids.empty?
+
+    details = [
+        "post_version_id=#{ version.id }",
+        "duplicate_tag_ids=#{ duplicate_tag_ids.inspect }"].join(', ')
+
+    raise "Duplicate tag IDs: #{ details }"
+  end
+end

backend/db/migrate/20260921000000_delete_inactive_records_from_post_tags.rb

@@ -0,0 +1,53 @@
+class DeleteInactiveRecordsFromPostTags < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      DELETE
+      FROM
+        post_tags
+      WHERE
+        discarded_at IS NOT NULL
+    SQL
+
+    remove_index :post_tags, [:tag_id, :discarded_at]
+    remove_index :post_tags, [:post_id, :discarded_at]
+    remove_index :post_tags, name: 'idx_post_tags_active_unique'
+    remove_index :post_tags, :discarded_at
+
+    remove_foreign_key :post_tags, column: :deleted_user_id
+    remove_index :post_tags, :deleted_user_id
+
+    remove_column :post_tags, :active_unique_key
+    remove_column :post_tags, :is_active
+    remove_column :post_tags, :discarded_at
+    remove_column :post_tags, :deleted_user_id
+    remove_column :post_tags, :updated_at
+
+    execute <<~SQL
+      ALTER TABLE
+        post_tags
+      MODIFY COLUMN
+        id BIGINT NOT NULL
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        post_tags
+      DROP PRIMARY KEY
+    SQL
+
+    remove_column :post_tags, :id
+
+    execute <<~SQL
+      ALTER TABLE
+        post_tags
+      ADD PRIMARY KEY
+        (post_id, tag_id)
+    SQL
+
+    remove_index :post_tags, :post_id
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+end

backend/db/migrate/20260921010000_add_foreign_key_on_post_id_and_tag_id_in_post_tag_sections.rb

@@ -0,0 +1,11 @@
+class AddForeignKeyOnPostIdAndTagIdInPostTagSections < ActiveRecord::Migration[8.0]
+  def change
+    remove_foreign_key :post_tag_sections, :posts, column: :post_id
+    remove_foreign_key :post_tag_sections, :tags, column: :tag_id
+
+    add_foreign_key :post_tag_sections, :post_tags,
+                    column: [:post_id, :tag_id],
+                    primary_key: [:post_id, :tag_id],
+                    on_delete: :cascade
+  end
+end

backend/db/migrate/20260921020000_delete_discarded_records_from_tags.rb

@@ -0,0 +1,46 @@
+class DeleteDiscardedRecordsFromTags < ActiveRecord::Migration[8.0]
+  def up
+    remove_foreign_key :tag_versions, :tags, column: :tag_id
+    remove_foreign_key :nico_tag_versions, :tags, column: :tag_id
+    remove_foreign_key :material_versions, :tags, column: :tag_id
+
+    execute <<~SQL
+      DELETE
+        ntr
+      FROM
+        nico_tag_relations ntr
+        INNER JOIN
+          tags t
+          ON
+            t.discarded_at IS NOT NULL
+            AND t.id IN (ntr.tag_id, ntr.nico_tag_id)
+    SQL
+
+    execute <<~SQL
+      DELETE
+        ti
+      FROM
+        tag_implications ti
+        INNER JOIN
+          tags t
+          ON
+            t.discarded_at IS NOT NULL
+            AND t.id IN (ti.tag_id, ti.parent_tag_id)
+    SQL
+
+    execute <<~SQL
+      DELETE
+      FROM
+        tags
+      WHERE
+        discarded_at IS NOT NULL
+    SQL
+
+    remove_index :tags, :discarded_at
+    remove_column :tags, :discarded_at
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+end

backend/db/migrate/20260921030000_delete_discarded_records_from_tag_names.rb

@@ -0,0 +1,18 @@
+class DeleteDiscardedRecordsFromTagNames < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      DELETE
+      FROM
+        tag_names
+      WHERE
+        discarded_at IS NOT NULL
+    SQL
+
+    remove_index :tag_names, :discarded_at
+    remove_column :tag_names, :discarded_at
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+end

backend/db/migrate/20260921040000_create_external_tags.rb

@@ -0,0 +1,54 @@
+class CreateExternalTags < ActiveRecord::Migration[8.0]
+  def up
+    create_table :external_tags do |t|
+      t.string :platform, limit: 16, null: false
+      t.string :name, limit: 255, null: false
+      t.integer :post_count, null: false, default: 0
+      t.datetime :created_at, null: false
+
+      t.index [:platform, :name], unique: true
+    end
+
+    execute <<~SQL
+      INSERT INTO
+        external_tags(id, platform, name, post_count, created_at)
+      SELECT
+        t.id
+      , 'nico' AS platform
+      , SUBSTR(tn.name, 6) AS name
+      , t.post_count
+      , t.created_at
+      FROM
+        tags t
+        INNER JOIN
+          tag_names tn
+          ON
+            tn.id = t.tag_name_id
+            AND t.category = 'nico'
+    SQL
+
+    execute <<~SQL
+      INSERT INTO
+        external_tags(id, platform, name, post_count, created_at)
+      SELECT
+        ntv.tag_id
+      , 'nico' AS platform
+      , SUBSTR(ntv.name, 6) AS name
+      , 0 AS post_count
+      , ntv.created_at
+      FROM
+        nico_tag_versions ntv
+        LEFT JOIN
+          external_tags et
+          ON
+            et.id = ntv.tag_id
+      WHERE
+        ntv.version_no = 1
+        AND et.id IS NULL
+    SQL
+  end
+
+  def down
+    drop_table :external_tags
+  end
+end

backend/db/migrate/20260921050000_create_post_external_tags.rb

@@ -0,0 +1,29 @@
+class CreatePostExternalTags < ActiveRecord::Migration[8.0]
+  def up
+    create_table :post_external_tags, primary_key: [:post_id, :external_tag_id] do |t|
+      t.references :post, null: false, index: false, foreign_key: true
+      t.references :external_tag, null: false, foreign_key: true
+      t.datetime :created_at, null: false
+    end
+
+    execute <<~SQL
+      INSERT INTO
+        post_external_tags(post_id, external_tag_id, created_at)
+      SELECT
+        pt.post_id
+      , pt.tag_id AS external_tag_id
+      , pt.created_at
+      FROM
+        post_tags pt
+        INNER JOIN
+          tags t
+          ON
+            pt.tag_id = t.id
+            AND t.category = 'nico'
+    SQL
+  end
+
+  def down
+    drop_table :post_external_tags
+  end
+end

backend/db/migrate/20260921060000_change_foreign_key_on_nico_tag_relations.rb

@@ -0,0 +1,6 @@
+class ChangeForeignKeyOnNicoTagRelations < ActiveRecord::Migration[8.0]
+  def change
+    remove_foreign_key :nico_tag_relations, :tags, column: :nico_tag_id
+    add_foreign_key :nico_tag_relations, :external_tags, column: :nico_tag_id
+  end
+end

backend/db/migrate/20260921230000_migrate_external_tags.rb

@@ -0,0 +1,199 @@
+class MigrateExternalTags < ActiveRecord::Migration[8.0]
+  class MigrationPostVersion < ActiveRecord::Base
+    self.table_name = 'post_versions'
+  end
+
+  def up
+    x = connection.select_value(<<~SQL)
+      SELECT
+        COUNT(0)
+      FROM
+        post_tag_sections pts
+      INNER JOIN
+        tags t
+        ON
+          t.id = pts.tag_id
+      WHERE
+        t.category = 'nico'
+    SQL
+    if x > 0
+      raise "post_tag_sections に #{ x } 件のチンカスがあります!"
+    end
+
+    x = connection.select_value(<<~SQL)
+      SELECT
+        COUNT(0)
+      FROM
+        materials m
+        INNER JOIN
+          tags t
+          ON
+            t.id = m.tag_id
+      WHERE
+        t.category = 'nico'
+    SQL
+    if x > 0
+      raise "materials に #{ x } 件のチンカスがあります!"
+    end
+
+    x = connection.select_value(<<~SQL)
+      SELECT
+        COUNT(0)
+      FROM
+        tag_implications ti
+        INNER JOIN
+          tags t
+          ON
+            t.id = ti.tag_id
+            OR t.id = ti.parent_tag_id
+      WHERE
+        t.category = 'nico'
+    SQL
+    if x > 0
+      raise "tag_implications に #{ x } 件のチンカスがあります!"
+    end
+
+    execute <<~SQL
+      DELETE
+        ts
+      FROM
+        tag_similarities ts
+        INNER JOIN
+          tags t
+          ON
+            t.category = 'nico'
+            AND (t.id = ts.tag_id
+                 OR t.id = ts.target_tag_id)
+    SQL
+
+    execute <<~SQL
+      DELETE
+        tset
+      FROM
+        theatre_skip_event_tags tset
+        INNER JOIN
+          tags t
+          ON
+            t.category = 'nico'
+            AND t.id = tset.tag_id
+    SQL
+
+    remove_check_constraint :post_versions, name: 'chk_post_versions_tags_json_schema'
+
+    say_with_time 'Migrate post_versions.tags_json' do
+      count = 0
+
+      MigrationPostVersion.find_each(batch_size: 500) do |version|
+        tags = version.tags_json.map do |tag|
+          if tag.fetch('category') == 'nico'
+            { 'external_tag_id' => tag.fetch('id') }
+          else
+            { 'tag_id' => tag.fetch('id'),
+              'version_no' => tag.fetch('version_no'),
+              'name' => tag.fetch('name'),
+              'category' => tag.fetch('category'),
+              'sections' => tag.fetch('sections') }
+          end
+        end
+
+        version.update_columns(tags_json: tags)
+        count += 1
+      end
+
+      count
+    end
+
+    add_tags_json_constraint!
+
+    tag_name_ids = connection.select_values(<<~SQL)
+      SELECT
+        tag_name_id
+      FROM
+        tags
+      WHERE
+        category = 'nico'
+    SQL
+
+    connection.transaction do
+      execute <<~SQL
+        DELETE
+          pt
+        FROM
+          post_tags pt
+          INNER JOIN
+            tags t
+            ON
+              t.category = 'nico'
+              AND t.id = pt.tag_id
+      SQL
+
+      execute <<~SQL
+        DELETE
+        FROM
+          tags
+        WHERE
+          category = 'nico'
+      SQL
+
+      unless tag_name_ids.empty?
+        execute <<~SQL
+          DELETE
+          FROM
+            tag_names
+          WHERE
+            id IN (#{ tag_name_ids.join(', ') })
+        SQL
+      end
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+
+  private
+
+  def add_tags_json_constraint!
+    schema = { type: 'array',
+               items: { oneOf: [internal_tag_schema, external_tag_schema] } }
+
+    quoted_schema = connection.quote(JSON.generate(schema))
+
+    add_check_constraint :post_versions,
+                         "JSON_SCHEMA_VALID(#{ quoted_schema }, tags_json)",
+                         name: 'chk_post_versions_tags_json_schema'
+  end
+
+  def internal_tag_schema
+    { type: 'object',
+      properties: { tag_id: { type: 'integer', minimum: 1 },
+                    version_no: { type: 'integer', minimum: 1 },
+                    name: { type: 'string', minLength: 1 },
+                    category: { type: 'string',
+                                enum: ['deerjikist',
+                                       'meme',
+                                       'character',
+                                       'general',
+                                       'material',
+                                       'meta'] },
+                    sections: sections_schema },
+      required: ['tag_id', 'version_no', 'sections'],
+      additionalProperties: false }
+  end
+
+  def external_tag_schema
+    { type: 'object',
+      properties: { external_tag_id: { type: 'integer', minimum: 1 } },
+      required: ['external_tag_id'],
+      additionalProperties: false }
+  end
+
+  def sections_schema
+    { type: 'array',
+      items: { type: 'object',
+               properties: { begin_ms: { type: 'integer', minimum: 0 },
+                             end_ms: { type: ['integer', 'null'], minimum: 0 } },
+               required: ['begin_ms', 'end_ms'],
+               additionalProperties: false } }
+  end
+end

backend/db/migrate/20260922000000_create_languages.rb

@@ -0,0 +1,20 @@
+class CreateLanguages < ActiveRecord::Migration[8.0]
+  def up
+    create_table :languages, id: { type: :string, limit: 16 }, primary_key: :code do |t|
+      t.string :name, null: false
+      t.datetime :deprecated_at, index: true
+      t.datetime :created_at, null: false
+    end
+
+    execute <<~SQL
+      INSERT INTO
+        languages(code, name, created_at)
+      VALUES
+        ('ja', '日本語', #{ connection.quote Time.current })
+    SQL
+  end
+
+  def down
+    drop_table :languages
+  end
+end

backend/db/migrate/20260922010000_create_scripts.rb

@@ -0,0 +1,23 @@
+class CreateScripts < ActiveRecord::Migration[8.0]
+  def up
+    create_table :scripts, id: { type: 'CHAR(4)' }, primary_key: :code do |t|
+      t.string :name, null: false
+      t.datetime :deprecated_at, index: true
+      t.datetime :created_at, null: false
+
+      t.check_constraint "REGEXP_LIKE(code, '^[A-Z][a-z]{3}$', 'c')",
+                         name: 'scripts_code_check'
+    end
+
+    execute <<~SQL
+      INSERT INTO
+        scripts(code, name, created_at)
+      VALUES
+        ('Jpan', '漢字、仮名文字およびラテン文字', #{ connection.quote Time.current })
+    SQL
+  end
+
+  def down
+    drop_table :scripts
+  end
+end

backend/db/migrate/20260922013000_create_regions.rb

@@ -0,0 +1,25 @@
+class CreateRegions < ActiveRecord::Migration[8.0]
+  def up
+    create_table :regions, id: { type: :integer, limit: 2 }, primary_key: :code do |t|
+      t.column :alpha_code, 'CHAR(2)'
+      t.string :name, null: false
+      t.datetime :deprecated_at, index: true
+      t.datetime :created_at, null: false
+
+      t.check_constraint "REGEXP_LIKE(alpha_code, '^[A-Z]{2}$', 'c')",
+                         name: 'regions_alpha_code_check'
+      t.index [:alpha_code], unique: true
+    end
+
+    execute <<~SQL
+      INSERT INTO
+        regions(code, alpha_code, name, created_at)
+      VALUES
+        (392, 'JP', '日本国', #{ connection.quote Time.current })
+    SQL
+  end
+
+  def down
+    drop_table :regions
+  end
+end

backend/db/migrate/20260922020000_create_locales.rb

@@ -0,0 +1,38 @@
+class CreateLocales < ActiveRecord::Migration[8.0]
+  def up
+    create_table :locales, id: { type: :string, limit: 32 }, primary_key: :code do |t|
+      t.string :language_code, limit: 16, null: false, index: true
+      t.column :script_code, 'CHAR(4)', null: false
+      t.integer :region_code, limit: 2, null: false
+      t.string :variants, limit: 255, null: false, default: ''
+      t.string :name, null: false
+      t.datetime :deprecated_at, index: true
+      t.datetime :created_at, null: false
+
+      t.foreign_key :languages, column: :language_code, primary_key: :code
+      t.foreign_key :scripts, column: :script_code, primary_key: :code
+      t.foreign_key :regions, column: :region_code, primary_key: :code
+      t.check_constraint ('REGEXP_LIKE(variants, ' +
+                          "'^(" +
+                          '(([a-z0-9]{5,8}|[0-9][a-z0-9]{3})' +
+                          '(-([a-z0-9]{5,8}|[0-9][a-z0-9]{3}))*' +
+                          '(-x(-[a-z0-9]{1,8})+)?)' +
+                          '|(x(-[a-z0-9]{1,8})+)' +
+                          ")?$', 'c')"),
+                         name: 'locales_variants_check'
+
+      t.index [:language_code, :script_code, :region_code, :variants], unique: true
+    end
+
+    execute <<~SQL
+      INSERT INTO
+        locales(code, language_code, script_code, region_code, name, created_at)
+      VALUES
+        ('ja', 'ja', 'Jpan', 392, '日本語', #{ connection.quote Time.current })
+    SQL
+  end
+
+  def down
+    drop_table :locales
+  end
+end

backend/db/migrate/20260922030000_add_columns_to_tag_names.rb

@@ -0,0 +1,69 @@
+class AddColumnsToTagNames < ActiveRecord::Migration[8.0]
+  def up
+    add_reference :tag_names, :tag, after: :id, foreign_key: true
+    add_column :tag_names, :language_code, :string,
+               limit: 16, null: false, after: :tag_id, default: 'ja'
+    add_column :tag_names, :script_code, 'CHAR(4)',
+               null: false, after: :name, default: 'Jpan'
+    add_column :tag_names, :primary_flg, :boolean,
+               null: false, after: :script_code, default: true
+    add_column :tag_names, :auto_generated, :boolean,
+               null: false, default: false, after: :primary_flg
+
+    add_foreign_key :tag_names, :languages, column: :language_code, primary_key: :code
+    add_foreign_key :tag_names, :scripts, column: :script_code, primary_key: :code
+
+    remove_index :tag_names, :name
+    add_index :tag_names, [:language_code, :name], unique: true
+
+    change_column_default :tag_names, :language_code, from: 'ja', to: nil
+    change_column_default :tag_names, :script_code, from: 'Jpan', to: nil
+
+    execute <<~SQL
+      UPDATE
+        tag_names tn
+        LEFT JOIN
+          tags AS t
+          ON
+            t.tag_name_id = COALESCE(tn.canonical_id, tn.id)
+      SET
+        tn.tag_id = t.id
+      , tn.primary_flg = CASE
+                         WHEN tn.canonical_id IS NULL THEN
+                           1
+                         ELSE
+                           0
+                         END
+    SQL
+
+    change_column_default :tag_names, :primary_flg, from: true, to: nil
+
+    add_column :tag_names, :primary_tag_id, :bigint,
+               as: 'CASE WHEN primary_flg THEN tag_id ELSE NULL END'
+    add_index :tag_names, [:primary_tag_id, :language_code], unique: true
+
+    add_check_constraint :tag_names,
+                         'primary_flg OR (NOT auto_generated)',
+                         name: 'chk_tag_names_auto_generated_primary'
+  end
+
+  def down
+    remove_check_constraint :tag_names,
+                            name: 'chk_tag_names_auto_generated_primary'
+
+    remove_index :tag_names, [:primary_tag_id, :language_code]
+    remove_column :tag_names, :primary_tag_id
+
+    remove_foreign_key :tag_names, column: :language_code
+    remove_foreign_key :tag_names, column: :script_code
+
+    remove_index :tag_names, [:language_code, :name]
+    add_index :tag_names, :name, unique: true
+
+    remove_column :tag_names, :auto_generated
+    remove_column :tag_names, :primary_flg
+    remove_column :tag_names, :script_code
+    remove_column :tag_names, :language_code
+    remove_reference :tag_names, :tag, foreign_key: true
+  end
+end

backend/db/migrate/20260922040000_add_names_to_tag_versions.rb

@@ -0,0 +1,68 @@
+class AddNamesToTagVersions < ActiveRecord::Migration[8.0]
+  class TagVersion < ActiveRecord::Base
+    self.table_name = 'tag_versions'
+  end
+
+  def up
+    add_column :tag_versions, :names, :json
+    TagVersion.reset_column_information
+
+    say_with_time 'Backfilling multilingual tag version names' do
+      TagVersion.find_each do |version|
+        aliases = version.aliases.to_s.split.filter_map do |name|
+          name.present? && { name:, script_code: 'Jpan' }
+        end
+        names = { ja: { name: version.name,
+                        script_code: 'Jpan',
+                        auto_generated: false,
+                        aliases: } }
+        version.update_columns(names:)
+      end
+    end
+
+    add_names_constraint!
+
+    change_column_null :tag_versions, :names, false
+  end
+
+  def down
+    remove_check_constraint :tag_versions,
+                            name: 'chk_tag_versions_names_schema'
+
+    remove_column :tag_versions, :names
+  end
+
+  private
+
+  def add_names_constraint!
+    schema = { type: 'object',
+               minProperties: 1,
+               patternProperties: { '^.{1,16}$': name_schema },
+               additionalProperties: false }
+
+    quoted_schema = connection.quote(JSON.generate(schema))
+
+    add_check_constraint :tag_versions,
+                         "JSON_SCHEMA_VALID(#{ quoted_schema }, names)",
+                         name: 'chk_tag_versions_names_schema'
+  end
+
+  def name_schema
+    { type: 'object',
+      required: ['name', 'script_code', 'auto_generated', 'aliases'],
+      properties: { **name_schema_base,
+                    auto_generated: { type: 'boolean' },
+                    aliases: { type: 'array',
+                               uniqueItems: true,
+                               items: { type: 'object',
+                                        required: ['name', 'script_code'],
+                                        properties: name_schema_base,
+                                        additionalProperties: false } } },
+      additionalProperties: false }
+  end
+
+  def name_schema_base
+    { name: { type: 'string', minLength: 1, maxLength: 255 },
+      script_code: { type: 'string', pattern: '^[A-Z][a-z]{3}$' } }
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
+ActiveRecord::Schema[8.0].define(version: 2026_09_22_040000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -48,6 +48,14 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.index ["tag_id"], name: "index_deerjikists_on_tag_id"
   end
 
+  create_table "external_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "platform", limit: 16, null: false
+    t.string "name", null: false
+    t.integer "post_count", default: 0, null: false
+    t.datetime "created_at", null: false
+    t.index ["platform", "name"], name: "index_external_tags_on_platform_and_name", unique: true
+  end
+
   create_table "gekanator_ai_runs", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "model", null: false
     t.integer "input_tokens", default: 0, null: false
@@ -130,6 +138,29 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.index ["ip_address"], name: "index_ip_addresses_on_ip_address", unique: true
   end
 
+  create_table "languages", primary_key: "code", id: { type: :string, limit: 16 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "name", null: false
+    t.datetime "deprecated_at"
+    t.datetime "created_at", null: false
+    t.index ["deprecated_at"], name: "index_languages_on_deprecated_at"
+  end
+
+  create_table "locales", primary_key: "code", id: { type: :string, limit: 32 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "language_code", limit: 16, null: false
+    t.string "script_code", limit: 4, null: false
+    t.integer "region_code", limit: 2, null: false
+    t.string "variants", default: "", null: false
+    t.string "name", null: false
+    t.datetime "deprecated_at"
+    t.datetime "created_at", null: false
+    t.index ["deprecated_at"], name: "index_locales_on_deprecated_at"
+    t.index ["language_code", "script_code", "region_code", "variants"], name: "idx_on_language_code_script_code_region_code_varian_b0ba85c39a", unique: true
+    t.index ["language_code"], name: "index_locales_on_language_code"
+    t.index ["region_code"], name: "fk_rails_175159992c"
+    t.index ["script_code"], name: "fk_rails_0b74ce96a8"
+    t.check_constraint "regexp_like(`variants`,_utf8mb4'^((([a-z0-9]{5,8}|[0-9][a-z0-9]{3})(-([a-z0-9]{5,8}|[0-9][a-z0-9]{3}))*(-x(-[a-z0-9]{1,8})+)?)|(x(-[a-z0-9]{1,8})+))?$',_utf8mb4'c')", name: "locales_variants_check"
+  end
+
   create_table "material_export_items", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "material_id", null: false
     t.string "profile", default: "legacy_drive", null: false
@@ -281,6 +312,13 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.check_constraint "`version_no` > 0", name: "nico_tag_versions_version_no_positive"
   end
 
+  create_table "post_external_tags", primary_key: ["post_id", "external_tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "post_id", null: false
+    t.bigint "external_tag_id", null: false
+    t.datetime "created_at", null: false
+    t.index ["external_tag_id"], name: "index_post_external_tags_on_external_tag_id"
+  end
+
   create_table "post_implications", primary_key: ["post_id", "parent_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "parent_post_id", null: false
@@ -311,23 +349,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
   end
 
-  create_table "post_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+  create_table "post_tags", primary_key: ["post_id", "tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
     t.bigint "created_user_id"
-    t.bigint "deleted_user_id"
     t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.datetime "discarded_at"
-    t.virtual "is_active", type: :boolean, as: "(`discarded_at` is null)", stored: true
-    t.virtual "active_unique_key", type: :string, as: "(case when (`discarded_at` is null) then concat(`post_id`,_utf8mb4':',`tag_id`) else NULL end)", stored: true
-    t.index ["active_unique_key"], name: "idx_post_tags_active_unique", unique: true
     t.index ["created_user_id"], name: "index_post_tags_on_created_user_id"
-    t.index ["deleted_user_id"], name: "index_post_tags_on_deleted_user_id"
-    t.index ["discarded_at"], name: "index_post_tags_on_discarded_at"
-    t.index ["post_id", "discarded_at"], name: "index_post_tags_on_post_id_and_discarded_at"
-    t.index ["post_id"], name: "index_post_tags_on_post_id"
-    t.index ["tag_id", "discarded_at"], name: "index_post_tags_on_tag_id_and_discarded_at"
     t.index ["tag_id"], name: "index_post_tags_on_tag_id"
   end
 
@@ -349,6 +376,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.string "url", limit: 768, null: false
     t.string "thumbnail_base", limit: 2000
     t.text "tags", null: false
+    t.json "tags_json", null: false
     t.text "parent_post_ids", null: false
     t.datetime "original_created_from"
     t.datetime "original_created_before"
@@ -362,6 +390,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_post_versions_video_ms_positive"
     t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
     t.check_constraint "`version_no` > 0", name: "post_versions_version_no_positive"
+    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"array\",\"items\":{\"oneOf\":[{\"type\":\"object\",\"properties\":{\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"version_no\":{\"type\":\"integer\",\"minimum\":1},\"name\":{\"type\":\"string\",\"minLength\":1},\"category\":{\"type\":\"string\",\"enum\":[\"deerjikist\",\"meme\",\"character\",\"general\",\"material\",\"meta\"]},\"sections\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"properties\":{\"begin_ms\":{\"type\":\"integer\",\"minimum\":0},\"end_ms\":{\"type\":[\"integer\",\"null\"],\"minimum\":0}},\"required\":[\"begin_ms\",\"end_ms\"],\"additionalProperties\":false}}},\"required\":[\"tag_id\",\"version_no\",\"sections\"],\"additionalProperties\":false},{\"type\":\"object\",\"properties\":{\"external_tag_id\":{\"type\":\"integer\",\"minimum\":1}},\"required\":[\"external_tag_id\"],\"additionalProperties\":false}]}}',`tags_json`)", name: "chk_post_versions_tags_json_schema"
   end
 
   create_table "posts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -382,6 +411,24 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
+  create_table "regions", primary_key: "code", id: { type: :integer, limit: 2 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "alpha_code", limit: 2
+    t.string "name", null: false
+    t.datetime "deprecated_at"
+    t.datetime "created_at", null: false
+    t.index ["alpha_code"], name: "index_regions_on_alpha_code", unique: true
+    t.index ["deprecated_at"], name: "index_regions_on_deprecated_at"
+    t.check_constraint "regexp_like(`alpha_code`,_utf8mb4'^[A-Z]{2}$',_utf8mb4'c')", name: "regions_alpha_code_check"
+  end
+
+  create_table "scripts", primary_key: "code", id: { type: :string, limit: 4 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "name", null: false
+    t.datetime "deprecated_at"
+    t.datetime "created_at", null: false
+    t.index ["deprecated_at"], name: "index_scripts_on_deprecated_at"
+    t.check_constraint "regexp_like(`code`,_utf8mb4'^[A-Z][a-z]{3}$',_utf8mb4'c')", name: "scripts_code_check"
+  end
+
   create_table "settings", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "user_id", null: false
     t.datetime "created_at", null: false
@@ -393,19 +440,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.index ["user_id"], name: "index_settings_on_user_id", unique: true
   end
 
-  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.bigint "wiki_page_id", null: false
-    t.integer "no", null: false
-    t.string "alt_text"
-    t.binary "sha256", limit: 32, null: false
-    t.bigint "created_by_user_id", null: false
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
-    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
-    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
-  end
-
   create_table "tag_implications", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_id", null: false
     t.bigint "parent_tag_id", null: false
@@ -427,14 +461,22 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   end
 
   create_table "tag_names", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id"
+    t.string "language_code", limit: 16, null: false
     t.string "name", null: false
+    t.string "script_code", limit: 4, null: false
+    t.boolean "primary_flg", null: false
+    t.boolean "auto_generated", default: false, null: false
     t.bigint "canonical_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.datetime "discarded_at"
+    t.virtual "primary_tag_id", type: :bigint, as: "(case when `primary_flg` then `tag_id` else NULL end)"
     t.index ["canonical_id"], name: "index_tag_names_on_canonical_id"
-    t.index ["discarded_at"], name: "index_tag_names_on_discarded_at"
-    t.index ["name"], name: "index_tag_names_on_name", unique: true
+    t.index ["language_code", "name"], name: "index_tag_names_on_language_code_and_name", unique: true
+    t.index ["primary_tag_id", "language_code"], name: "index_tag_names_on_primary_tag_id_and_language_code", unique: true
+    t.index ["script_code"], name: "fk_rails_dd783b3d1c"
+    t.index ["tag_id"], name: "index_tag_names_on_tag_id"
+    t.check_constraint "(0 <> `primary_flg`) or (0 = `auto_generated`)", name: "chk_tag_names_auto_generated_primary"
   end
 
   create_table "tag_similarities", primary_key: ["tag_id", "target_tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -456,11 +498,13 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.datetime "deprecated_at"
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
+    t.json "names", null: false
     t.index ["created_at"], name: "index_tag_versions_on_created_at"
     t.index ["created_by_user_id", "created_at"], name: "index_tag_versions_on_created_by_user_id_and_created_at", order: { created_at: :desc }
     t.index ["tag_id", "created_at"], name: "index_tag_versions_on_tag_id_and_created_at", order: { created_at: :desc }
     t.index ["tag_id", "version_no"], name: "index_tag_versions_on_tag_id_and_version_no", unique: true
     t.check_constraint "`version_no` > 0", name: "tag_versions_version_no_positive"
+    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"object\",\"minProperties\":1,\"patternProperties\":{\"^.{1,16}$\":{\"type\":\"object\",\"required\":[\"name\",\"script_code\",\"auto_generated\",\"aliases\"],\"properties\":{\"name\":{\"type\":\"string\",\"minLength\":1,\"maxLength\":255},\"script_code\":{\"type\":\"string\",\"pattern\":\"^[A-Z][a-z]{3}$\"},\"auto_generated\":{\"type\":\"boolean\"},\"aliases\":{\"type\":\"array\",\"uniqueItems\":true,\"items\":{\"type\":\"object\",\"required\":[\"name\",\"script_code\"],\"properties\":{\"name\":{\"type\":\"string\",\"minLength\":1,\"maxLength\":255},\"script_code\":{\"type\":\"string\",\"pattern\":\"^[A-Z][a-z]{3}$\"}},\"additionalProperties\":false}}},\"additionalProperties\":false}},\"additionalProperties\":false}',`names`)", name: "chk_tag_versions_names_schema"
   end
 
   create_table "tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -470,10 +514,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
-    t.datetime "discarded_at"
     t.integer "version_no", null: false
     t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
-    t.index ["discarded_at"], name: "index_tags_on_discarded_at"
     t.index ["tag_name_id"], name: "index_tags_on_tag_name_id", unique: true
     t.check_constraint "(`deprecated_at` is null) or (`category` <> _utf8mb4'nico')", name: "chk_tags_deprecated_at_not_nico"
     t.check_constraint "`version_no` > 0", name: "chk_tags_version_no_positive"
@@ -614,6 +656,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.index ["banned_at"], name: "index_users_on_banned_at"
   end
 
+  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_page_id", null: false
+    t.integer "no", null: false
+    t.string "alt_text"
+    t.binary "sha256", limit: 32, null: false
+    t.bigint "created_by_user_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
+    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
+    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
+  end
+
   create_table "wiki_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "sha256", limit: 64, null: false
     t.text "body", null: false
@@ -699,6 +754,9 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   add_foreign_key "gekanator_question_suggestions", "users"
   add_foreign_key "gekanator_questions", "gekanator_question_suggestions"
   add_foreign_key "gekanator_questions", "users", column: "created_by_id"
+  add_foreign_key "locales", "languages", column: "language_code", primary_key: "code"
+  add_foreign_key "locales", "regions", column: "region_code", primary_key: "code"
+  add_foreign_key "locales", "scripts", column: "script_code", primary_key: "code"
   add_foreign_key "material_export_items", "materials"
   add_foreign_key "material_export_items", "users", column: "created_by_user_id"
   add_foreign_key "material_import_blocks", "users", column: "created_by_user_id"
@@ -707,37 +765,37 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   add_foreign_key "material_sync_suppressions", "users", column: "created_by_user_id"
   add_foreign_key "material_versions", "materials"
   add_foreign_key "material_versions", "materials", column: "parent_id"
-  add_foreign_key "material_versions", "tags"
   add_foreign_key "material_versions", "users", column: "created_by_user_id"
   add_foreign_key "material_versions", "users", column: "updated_by_user_id"
   add_foreign_key "materials", "materials", column: "parent_id"
   add_foreign_key "materials", "tags"
   add_foreign_key "materials", "users", column: "created_by_user_id"
   add_foreign_key "materials", "users", column: "updated_by_user_id"
+  add_foreign_key "nico_tag_relations", "external_tags", column: "nico_tag_id"
   add_foreign_key "nico_tag_relations", "tags"
-  add_foreign_key "nico_tag_relations", "tags", column: "nico_tag_id"
-  add_foreign_key "nico_tag_versions", "tags"
   add_foreign_key "nico_tag_versions", "users", column: "created_by_user_id"
+  add_foreign_key "post_external_tags", "external_tags"
+  add_foreign_key "post_external_tags", "posts"
   add_foreign_key "post_implications", "posts"
   add_foreign_key "post_implications", "posts", column: "parent_post_id"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
-  add_foreign_key "post_tag_sections", "posts"
-  add_foreign_key "post_tag_sections", "tags"
+  add_foreign_key "post_tag_sections", "post_tags", column: ["post_id", "tag_id"], primary_key: ["post_id", "tag_id"], on_delete: :cascade
   add_foreign_key "post_tags", "posts"
   add_foreign_key "post_tags", "tags"
   add_foreign_key "post_tags", "users", column: "created_user_id"
-  add_foreign_key "post_tags", "users", column: "deleted_user_id"
   add_foreign_key "post_versions", "posts"
   add_foreign_key "post_versions", "users", column: "created_by_user_id"
   add_foreign_key "posts", "users", column: "uploaded_user_id"
   add_foreign_key "settings", "users"
   add_foreign_key "tag_implications", "tags"
   add_foreign_key "tag_implications", "tags", column: "parent_tag_id"
+  add_foreign_key "tag_names", "languages", column: "language_code", primary_key: "code"
+  add_foreign_key "tag_names", "scripts", column: "script_code", primary_key: "code"
   add_foreign_key "tag_names", "tag_names", column: "canonical_id"
+  add_foreign_key "tag_names", "tags"
   add_foreign_key "tag_similarities", "tags"
   add_foreign_key "tag_similarities", "tags", column: "target_tag_id"
-  add_foreign_key "tag_versions", "tags"
   add_foreign_key "tag_versions", "users", column: "created_by_user_id"
   add_foreign_key "tags", "tag_names"
   add_foreign_key "theatre_comments", "theatres"

backend/lib/tasks/sync_nico.rake

@@ -16,7 +16,7 @@ namespace :nico do
     end
 
     def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
-      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      current_tag_ids ||= PostTag.where(post_id: post.id).pluck(:tag_id).to_set
       desired_tag_ids = desired_tag_ids.compact.to_set
 
       to_add = desired_tag_ids - current_tag_ids
@@ -30,9 +30,28 @@ namespace :nico do
         end
       end
 
-      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
-        pt.discard_by!(nil)
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each(&:destroy!)
+    end
+
+    def sync_post_external_tags! post, desired_external_tag_ids, current_external_tag_ids: nil
+      current_external_tag_ids ||=
+          PostExternalTag.where(post_id: post.id).pluck(:external_tag_id).to_set
+      desired_external_tag_ids = desired_external_tag_ids.compact.to_set
+
+      to_add = desired_external_tag_ids - current_external_tag_ids
+      to_remove = current_external_tag_ids - desired_external_tag_ids
+
+      ExternalTag.where(id: to_add.to_a).find_each do |external_tag|
+        begin
+          PostExternalTag.create!(post:, external_tag:)
+        rescue ActiveRecord::RecordNotUnique
+          ;
+        end
       end
+
+      PostExternalTag
+          .where(post_id: post.id, external_tag_id: to_remove.to_a)
+          .find_each(&:destroy!)
     end
 
     mysql_user = ENV['MYSQL_USER']
@@ -111,58 +130,64 @@ namespace :nico do
         sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.niconico.id, Tag.video.id])
       end
 
-      tags = post.tags
       # 既存のタグ Id. 集合
-      kept_tag_ids = tags.pluck(:id).to_set
-      # うち内部タグ Id. 集合
-      kept_non_nico_tag_ids = tags.not_nico.pluck(:id).to_set
+      kept_tag_ids = post.tags.pluck(:id).to_set
+
+      # 既存の外部タグ Id. 集合
+      kept_external_tag_ids = post.external_tags.nico.pluck(:id).to_set
+
+      # 記載すべき外部タグ Id. のリスト
+      desired_external_tag_ids = []
 
-      # 記載すべき外部タグ Id. および連携される内部タグ Id. のリスト
-      desired_nico_tag_based_ids = []
       # 記載すべき内部タグ Id. のリスト
-      desired_non_nico_tag_ids = []
+      desired_tag_ids = kept_tag_ids.to_a
 
       datum['tags'].each do |raw|
-        name = TagNameSanitisationRule.sanitise("nico:#{ raw }")
-        tag = Tag.find_or_create_by_tag_name!(name, category: :nico)
+        name = TagNameSanitisationRule.sanitise("nico:#{ raw }").delete_prefix('nico:')
+        tag = ExternalTag.find_or_create_by!(platform: :nico, name:)
 
-        event_type = tag.nico_tag_versions.exists? ? :update : :create
-        NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user: nil)
+        unless tag.nico_tag_versions.exists?
+          NicoTagVersionRecorder.record!(external_tag: tag,
+                                         event_type: :create,
+                                         created_by_user: nil)
+        end
 
-        desired_nico_tag_based_ids << tag.id
+        desired_external_tag_ids << tag.id
 
         # 新たに記載される外部タグと連携される内部タグを記載
-        unless tag.id.in?(kept_tag_ids)
-          linked_ids = tag.linked_tags.pluck(:id)
-          desired_non_nico_tag_ids.concat(linked_ids)
-          desired_nico_tag_based_ids.concat(linked_ids)
+        # 連携タグは記載すれども消除せず．
+        unless tag.id.in?(kept_external_tag_ids)
+          desired_tag_ids.concat(tag.linked_tags.pluck(:id))
         end
       end
 
       deerjikist = Deerjikist.find_by(platform: :nico, code: datum['user'])
       if deerjikist
-        desired_non_nico_tag_ids << deerjikist.tag_id
-        desired_nico_tag_based_ids << deerjikist.tag_id
-      elsif !(Tag.where(id: kept_non_nico_tag_ids).where(category: :deerjikist).exists?)
-        desired_non_nico_tag_ids << Tag.no_deerjikist.id
-        desired_nico_tag_based_ids << Tag.no_deerjikist.id
+        desired_tag_ids << deerjikist.tag_id
+      elsif !(Tag.where(id: kept_tag_ids).where(category: :deerjikist).exists?)
+        desired_tag_ids << Tag.no_deerjikist.id
       end
 
-      desired_nico_tag_based_ids.uniq!
+      desired_external_tag_ids.uniq!
+      desired_tag_ids.uniq!
 
-      desired_all_tag_ids = kept_non_nico_tag_ids.to_a + desired_nico_tag_based_ids
-      desired_non_nico_tag_ids.concat(kept_non_nico_tag_ids.to_a)
-      desired_non_nico_tag_ids.uniq!
-      if kept_non_nico_tag_ids != desired_non_nico_tag_ids.to_set
-        desired_all_tag_ids << Tag.bot.id
+      # 外部タグの記載に際しては “bot 操作” タグを記載しなぃ．
+      if kept_tag_ids != desired_tag_ids.to_set
+        desired_tag_ids << Tag.bot.id
+        desired_tag_ids.uniq!
       end
-      desired_all_tag_ids.uniq!
 
-      sync_post_tags!(post, desired_all_tag_ids, current_tag_ids: kept_tag_ids)
+      tags_changed =
+          kept_tag_ids != desired_tag_ids.to_set ||
+          kept_external_tag_ids != desired_external_tag_ids.to_set
+
+      sync_post_tags!(post, desired_tag_ids, current_tag_ids: kept_tag_ids)
+      sync_post_external_tags!(post, desired_external_tag_ids,
+                               current_external_tag_ids: kept_external_tag_ids)
 
       if post_created
         PostVersionRecorder.record!(post:, event_type: :create, created_by_user: nil)
-      elsif post_changed || kept_tag_ids != desired_all_tag_ids.to_set
+      elsif post_changed || tags_changed
         PostVersionRecorder.ensure_snapshot!(post, created_by_user: nil)
         PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
       end

backend/spec/db/delete_discarded_tags_spec.rb

@@ -0,0 +1,124 @@
+require 'rails_helper'
+require_relative '../../db/migrate/20260921020000_delete_discarded_records_from_tags'
+require_relative '../../db/migrate/20260921030000_delete_discarded_records_from_tag_names'
+
+RSpec.describe 'discarded tag cleanup migrations' do
+  [DeleteDiscardedRecordsFromTags, DeleteDiscardedRecordsFromTagNames].each do |migration_class|
+    it "rejects rollback of #{ migration_class.name }" do
+      expect { migration_class.new.down }
+          .to raise_error(ActiveRecord::IrreversibleMigration)
+    end
+  end
+
+  context 'with legacy records' do
+    # Reproduce the historical schema required by these pre-multilingual migrations.
+    self.use_transactional_tests = false
+
+    before do
+      record_class = Class.new(ActiveRecord::Base) do
+        self.abstract_class = true
+      end
+      stub_const('TagCleanupMigrationRecord', record_class)
+      config = ActiveRecord::Base.connection_db_config.configuration_hash
+      @database = "btrc_hub_test_tag_cleanup_#{ Process.pid }_#{ SecureRandom.hex(4) }"
+      record_class.establish_connection(config.merge(database: nil))
+      @connection = record_class.lease_connection
+      @connection.create_database(@database)
+      @database_created = true
+      @connection.execute("USE #{ @connection.quote_table_name(@database) }")
+    end
+
+    after do
+      @connection.drop_database(@database) if @database_created
+    ensure
+      TagCleanupMigrationRecord.remove_connection
+    end
+
+    before do
+      @connection.create_table(:tag_names) do |t|
+        t.string :name, null: false, index: { unique: true }
+        t.bigint :canonical_id
+        t.datetime :discarded_at, index: true
+      end
+      @connection.add_foreign_key(:tag_names, :tag_names, column: :canonical_id)
+      @connection.create_table(:tags) do |t|
+        t.references :tag_name, null: false, foreign_key: true, index: { unique: true }
+        t.datetime :discarded_at, index: true
+      end
+      @connection.create_table(:nico_tag_relations) do |t|
+        t.references :tag, null: false, foreign_key: true
+        t.references :nico_tag, null: false, foreign_key: { to_table: :tags }
+      end
+      @connection.create_table(:tag_implications) do |t|
+        t.references :tag, null: false, foreign_key: true
+        t.references :parent_tag, null: false, foreign_key: { to_table: :tags }
+      end
+      [:tag_versions, :nico_tag_versions, :material_versions].each do |table|
+        @connection.create_table(table) do |t|
+          t.references :tag, null: false, foreign_key: true
+        end
+      end
+
+      @connection.execute(<<~SQL)
+        INSERT INTO tag_names (id, name, canonical_id, discarded_at) VALUES
+          (1, 'kept', NULL, NULL),
+          (2, 'merged_alias', 1, NULL),
+          (3, 'nico:deleted', NULL, '2026-09-20'),
+          (4, 'nico:kept', NULL, NULL),
+          (5, 'deleted_name', NULL, '2026-09-20')
+      SQL
+      @connection.execute(<<~SQL)
+        INSERT INTO tags (id, tag_name_id, discarded_at) VALUES
+          (1, 1, NULL), (2, 2, '2026-09-20'),
+          (3, 3, '2026-09-20'), (4, 4, NULL)
+      SQL
+      @connection.execute(<<~SQL)
+        INSERT INTO nico_tag_relations (id, tag_id, nico_tag_id) VALUES
+          (1, 1, 4), (2, 2, 4), (3, 1, 3), (4, 2, 3)
+      SQL
+      @connection.execute(<<~SQL)
+        INSERT INTO tag_implications (id, tag_id, parent_tag_id) VALUES
+          (1, 1, 4), (2, 2, 1), (3, 1, 2), (4, 2, 3)
+      SQL
+      @connection.execute('INSERT INTO tag_versions (tag_id) VALUES (1), (2)')
+      @connection.execute('INSERT INTO nico_tag_versions (tag_id) VALUES (3), (4)')
+      @connection.execute('INSERT INTO material_versions (tag_id) VALUES (1), (2)')
+    end
+
+    it 'removes discarded records and their links while retaining aliases and history' do
+      [DeleteDiscardedRecordsFromTags, DeleteDiscardedRecordsFromTagNames].each do |klass|
+        migration = klass.new
+        allow(migration).to receive(:connection).and_return(@connection)
+        migration.suppress_messages { migration.up }
+      end
+
+      expect(@connection.select_values('SELECT id FROM tags ORDER BY id')).to eq([1, 4])
+      expect(@connection.select_rows('SELECT id, canonical_id FROM tag_names ORDER BY id'))
+          .to eq([[1, nil], [2, 1], [4, nil]])
+      expect(@connection.select_values('SELECT id FROM nico_tag_relations')).to eq([1])
+      expect(@connection.select_values('SELECT id FROM tag_implications')).to eq([1])
+      expect(@connection.select_values('SELECT tag_id FROM tag_versions ORDER BY tag_id'))
+          .to eq([1, 2])
+      expect(@connection.select_values('SELECT tag_id FROM nico_tag_versions ORDER BY tag_id'))
+          .to eq([3, 4])
+      expect(@connection.select_values('SELECT tag_id FROM material_versions ORDER BY tag_id'))
+          .to eq([1, 2])
+
+      [:tags, :tag_names].each do |table|
+        expect(@connection.column_exists?(table, :discarded_at)).to be(false)
+        expect(@connection.index_exists?(table, :discarded_at)).to be(false)
+      end
+      [:tag_versions, :nico_tag_versions, :material_versions].each do |table|
+        expect(@connection.foreign_key_exists?(table, :tags, column: :tag_id)).to be(false)
+      end
+      expect(@connection.foreign_key_exists?(:tags, :tag_names)).to be(true)
+      expect(@connection.foreign_key_exists?(:tag_names, :tag_names, column: :canonical_id))
+          .to be(true)
+      expect(@connection.index_exists?(:tag_names, :name, unique: true)).to be(true)
+      expect(@connection.index_exists?(:tags, :tag_name_id, unique: true)).to be(true)
+      [:nico_tag_relations, :tag_implications].each do |table|
+        expect(@connection.foreign_keys(table).map(&:to_table)).to eq(['tags', 'tags'])
+      end
+    end
+  end
+end

backend/spec/db/external_tags_spec.rb

@@ -0,0 +1,191 @@
+require 'rails_helper'
+require_relative '../../db/migrate/20260921040000_create_external_tags'
+require_relative '../../db/migrate/20260921050000_create_post_external_tags'
+require_relative '../../db/migrate/20260921060000_change_foreign_key_on_nico_tag_relations'
+require_relative '../../db/migrate/20260921230000_migrate_external_tags'
+
+RSpec.describe 'external tag migrations' do
+  self.use_transactional_tests = false
+
+  before do
+    record_class = Class.new(ActiveRecord::Base) do
+      self.abstract_class = true
+    end
+    stub_const('ExternalTagMigrationRecord', record_class)
+    config = ActiveRecord::Base.connection_db_config.configuration_hash
+    @database = "btrc_hub_test_external_tags_#{ Process.pid }_#{ SecureRandom.hex(4) }"
+    record_class.establish_connection(config.merge(database: nil))
+    @connection = record_class.lease_connection
+    @connection.create_database(@database)
+    @database_created = true
+    @connection.execute("USE #{ @connection.quote_table_name(@database) }")
+    version_class = Class.new(record_class) do
+      self.table_name = 'post_versions'
+    end
+    stub_const('MigrateExternalTags::MigrationPostVersion', version_class)
+    create_legacy_tables
+    seed_legacy_records
+  end
+
+  after do
+    @connection.drop_database(@database) if @database_created
+  ensure
+    ExternalTagMigrationRecord.remove_connection
+  end
+
+  def migrate klass
+    migration = klass.new
+    allow(migration).to receive(:connection).and_return(@connection)
+    migration.suppress_messages { migration.migrate(:up) }
+  end
+
+  def create_legacy_tables
+    @connection.create_table(:tag_names) { |t| t.string :name }
+    @connection.create_table(:tags) do |t|
+      t.references :tag_name, foreign_key: true
+      t.string :category
+      t.integer :post_count
+      t.datetime :created_at
+    end
+    @connection.create_table(:posts)
+    @connection.create_table(:post_tags) do |t|
+      t.references :post, foreign_key: true
+      t.references :tag, foreign_key: true
+      t.datetime :created_at
+    end
+    @connection.create_table(:nico_tag_versions) do |t|
+      t.bigint :tag_id
+      t.integer :version_no
+      t.string :name
+      t.datetime :created_at
+    end
+    @connection.create_table(:nico_tag_relations) do |t|
+      t.references :tag, foreign_key: true
+      t.references :nico_tag, foreign_key: { to_table: :tags }
+    end
+    [:post_tag_sections, :materials, :theatre_skip_event_tags].each do |table|
+      @connection.create_table(table) { |t| t.references :tag, foreign_key: true }
+    end
+    @connection.create_table(:tag_implications) do |t|
+      t.references :tag, foreign_key: true
+      t.references :parent_tag, foreign_key: { to_table: :tags }
+    end
+    @connection.create_table(:tag_similarities) do |t|
+      t.references :tag, foreign_key: true
+      t.references :target_tag, foreign_key: { to_table: :tags }
+    end
+    @connection.create_table(:post_versions) { |t| t.json :tags_json, null: false }
+    @connection.add_check_constraint(:post_versions, 'JSON_VALID(tags_json)',
+                                     name: 'chk_post_versions_tags_json_schema')
+  end
+
+  def seed_legacy_records
+    @connection.execute(<<~SQL)
+      INSERT INTO tag_names (id, name) VALUES (1, 'internal'), (2, 'nico:raw tag[]');
+    SQL
+    @connection.execute(<<~SQL)
+      INSERT INTO tags (id, tag_name_id, category, post_count, created_at) VALUES
+        (1, 1, 'general', 1, '2026-09-01'), (2, 2, 'nico', 1, '2026-09-02')
+    SQL
+    @connection.execute('INSERT INTO posts (id) VALUES (1)')
+    @connection.execute(<<~SQL)
+      INSERT INTO post_tags (post_id, tag_id, created_at) VALUES
+        (1, 1, '2026-09-03'), (1, 2, '2026-09-04')
+    SQL
+    @connection.execute(<<~SQL)
+      INSERT INTO nico_tag_versions (tag_id, version_no, name, created_at) VALUES
+        (2, 1, 'nico:raw tag[]', '2026-09-02'),
+        (3, 1, 'nico:deleted', '2026-09-01'),
+        (3, 2, 'nico:deleted_later', '2026-09-02')
+    SQL
+    @connection.execute('INSERT INTO nico_tag_relations (tag_id, nico_tag_id) VALUES (1, 2)')
+    @connection.execute(<<~SQL)
+      INSERT INTO tag_similarities (tag_id, target_tag_id) VALUES (1, 1), (1, 2), (2, 1)
+    SQL
+    @connection.execute('INSERT INTO theatre_skip_event_tags (tag_id) VALUES (1), (2)')
+    @legacy_internal = { 'id' => 1, 'version_no' => 2,
+                         'name' => 'internal', 'category' => 'general',
+                         'sections' => [{ 'begin_ms' => 1000, 'end_ms' => nil }] }
+    snapshots = [@legacy_internal,
+                 { 'id' => 2, 'category' => 'nico' },
+                 { 'id' => 3, 'category' => 'nico' }]
+    @connection.execute(<<~SQL)
+      INSERT INTO post_versions (tags_json) VALUES
+        (#{ @connection.quote(snapshots.to_json) }), ('[]')
+    SQL
+  end
+
+  def prepare_external_tables
+    migrate(CreateExternalTags)
+    migrate(CreatePostExternalTags)
+    migrate(ChangeForeignKeyOnNicoTagRelations)
+  end
+
+  it 'preserves ids, raw names, counts, timestamps, post links and historical-only tags' do
+    prepare_external_tables
+
+    rows = @connection.select_rows(<<~SQL)
+      SELECT id, platform, name, post_count, DATE_FORMAT(created_at, '%Y-%m-%d')
+      FROM external_tags ORDER BY id
+    SQL
+    expect(rows).to eq([
+        [2, 'nico', 'raw tag[]', 1, '2026-09-02'],
+        [3, 'nico', 'deleted', 0, '2026-09-01']])
+    expect(@connection.select_rows(<<~SQL)).to eq([[1, 2, '2026-09-04']])
+      SELECT post_id, external_tag_id, DATE_FORMAT(created_at, '%Y-%m-%d')
+      FROM post_external_tags
+    SQL
+    expect(@connection.foreign_key_exists?(:nico_tag_relations, :external_tags,
+                                           column: :nico_tag_id)).to be(true)
+    expect(@connection.foreign_key_exists?(:nico_tag_relations, :tags,
+                                           column: :tag_id)).to be(true)
+  end
+
+  it 'converts snapshots and removes only obsolete internal rows and derived links' do
+    prepare_external_tables
+    migrate(MigrateExternalTags)
+
+    expect(@connection.select_values('SELECT id FROM tags')).to eq([1])
+    expect(@connection.select_values('SELECT id FROM tag_names')).to eq([1])
+    expect(@connection.select_values('SELECT tag_id FROM post_tags')).to eq([1])
+    expect(@connection.select_rows('SELECT tag_id, nico_tag_id FROM nico_tag_relations'))
+        .to eq([[1, 2]])
+    expect(@connection.select_rows('SELECT tag_id, target_tag_id FROM tag_similarities'))
+        .to eq([[1, 1]])
+    expect(@connection.select_values('SELECT tag_id FROM theatre_skip_event_tags')).to eq([1])
+    expect(@connection.select_value('SELECT COUNT(*) FROM nico_tag_versions')).to eq(3)
+    versions = MigrateExternalTags::MigrationPostVersion.order(:id)
+    expect(versions.first.tags_json).to eq([
+        @legacy_internal.except('id').merge('tag_id' => 1),
+        { 'external_tag_id' => 2 }, { 'external_tag_id' => 3 }])
+    expect(versions.last.tags_json).to eq([])
+
+    invalid_snapshots = [@legacy_internal,
+                         { 'external_tag_id' => 0 },
+                         { 'external_tag_id' => 2, 'tag_id' => 1 },
+                         { 'external_tag_id' => 2, 'name' => 'extra' },
+                         { 'tag_id' => 1, 'version_no' => 1 }]
+    invalid_snapshots.each do |snapshot|
+      expect {
+        MigrateExternalTags::MigrationPostVersion.create!(tags_json: [snapshot])
+      }.to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+    end
+    expect { MigrateExternalTags.new.down }
+        .to raise_error(ActiveRecord::IrreversibleMigration)
+  end
+
+  { post_tag_sections: '(tag_id) VALUES (2)',
+    materials: '(tag_id) VALUES (2)',
+    tag_implications: '(tag_id, parent_tag_id) VALUES (1, 2)' }.each do |table, values|
+    it "aborts before deleting data when #{ table } references a legacy nico tag" do
+      prepare_external_tables
+      @connection.execute("INSERT INTO #{ table } #{ values }")
+
+      expect { migrate(MigrateExternalTags) }.to raise_error(RuntimeError, /#{ table }/)
+
+      expect(@connection.select_values('SELECT id FROM tags ORDER BY id')).to eq([1, 2])
+      expect(MigrateExternalTags::MigrationPostVersion.first.tags_json.first)
+          .to eq(@legacy_internal)
+    end
+  end
+end

backend/spec/db/tag_name_constraints_spec.rb

@@ -0,0 +1,36 @@
+require 'rails_helper'
+
+RSpec.describe 'TagName database invariants' do
+  def insert_name!(**attributes)
+    TagName.insert_all!([{ name: 'constraint_name', language_code: 'ja',
+                          script_code: 'Jpan', primary_flg: true,
+                          created_at: Time.current, updated_at: Time.current,
+                          **attributes }])
+  end
+
+  it 'defaults persisted names to human-confirmed provenance' do
+    insert_name!
+
+    expect(TagName.find_by!(name: 'constraint_name').auto_generated).to be(false)
+  end
+
+  [[true, true], [true, false], [false, false]].each do |primary_flg, auto_generated|
+    it "allows primary=#{ primary_flg }, auto_generated=#{ auto_generated }" do
+      expect { insert_name!(primary_flg:, auto_generated:) }
+          .to change(TagName, :count).by(1)
+    end
+  end
+
+  it 'rejects auto-generated aliases at the database boundary' do
+    expect { insert_name!(primary_flg: false, auto_generated: true) }
+        .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+  end
+
+  it 'rejects a second primary for the same tag and language' do
+    tag = create(:tag)
+
+    expect { insert_name!(tag_id: tag.id, auto_generated: false) }
+        .to raise_error(ActiveRecord::RecordNotUnique)
+    expect(TagName.where(tag:, language_code: 'ja', primary_flg: true).count).to eq(1)
+  end
+end

backend/spec/db/tag_version_names_spec.rb

@@ -0,0 +1,91 @@
+require 'rails_helper'
+
+RSpec.describe 'TagVersion names database constraint' do
+  let(:tag) { create(:tag) }
+  let(:names) do
+    { 'ja' => { 'name' => 'snapshot_name', 'script_code' => 'Jpan',
+                'auto_generated' => false, 'aliases' => [] } }
+  end
+  let(:alias_name) { { 'name' => 'snapshot_alias', 'script_code' => 'Jpan' } }
+
+  def insert_snapshot!(snapshot)
+    TagVersion.insert_all!([{ tag_id: tag.id, version_no: 1, event_type: 'create',
+                             name: 'snapshot_name', category: 'general',
+                             aliases: '', parent_tag_ids: '', names: snapshot,
+                             created_at: Time.current }])
+  end
+
+  it 'accepts grouped Nipponese names with an empty alias list' do
+    expect { insert_snapshot!(names) }.to change(TagVersion, :count).by(1)
+    expect(TagVersion.find_by!(tag_id: tag.id).names).to eq(names)
+  end
+
+  it 'accepts aliases containing only their name and script' do
+    names['ja']['aliases'] = [alias_name]
+
+    expect { insert_snapshot!(names) }.to change(TagVersion, :count).by(1)
+  end
+
+  it 'rejects a flat array root' do
+    expect { insert_snapshot!([names.fetch('ja')]) }
+        .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+  end
+
+  it 'rejects an empty object root' do
+    expect { insert_snapshot!({ }) }
+        .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+  end
+
+  it 'rejects a language entry that is not an object' do
+    expect { insert_snapshot!({ 'ja' => 'not an object' }) }
+        .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+  end
+
+  ['name', 'script_code', 'auto_generated', 'aliases'].each do |field|
+    it "rejects a primary entry missing #{ field }" do
+      names['ja'].delete(field)
+
+      expect { insert_snapshot!(names) }
+          .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+    end
+  end
+
+  it 'rejects an empty primary name' do
+    names['ja']['name'] = ''
+
+    expect { insert_snapshot!(names) }
+        .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+  end
+
+  it 'rejects incorrect script casing' do
+    names['ja']['script_code'] = 'JPAN'
+
+    expect { insert_snapshot!(names) }
+        .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+  end
+
+  ['unknown', 'primary_flg', 'language_code'].each do |field|
+    it "rejects the extra primary field #{ field }" do
+      names['ja'][field] = true
+
+      expect { insert_snapshot!(names) }
+          .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+    end
+  end
+
+  ['unknown', 'primary_flg', 'auto_generated'].each do |field|
+    it "rejects the extra alias field #{ field }" do
+      names['ja']['aliases'] = [alias_name.merge(field => true)]
+
+      expect { insert_snapshot!(names) }
+          .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+    end
+  end
+
+  it 'rejects duplicate alias objects' do
+    names['ja']['aliases'] = [alias_name, alias_name.deep_dup]
+
+    expect { insert_snapshot!(names) }
+        .to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
+  end
+end

backend/spec/factories/external_tags.rb

@@ -0,0 +1,6 @@
+FactoryBot.define do
+  factory :external_tag do
+    platform { :nico }
+    sequence(:name) { |n| "external_tag_#{ n }" }
+  end
+end

backend/spec/factories/tag_names.rb

@@ -1,5 +1,13 @@
 FactoryBot.define do
   factory :tag_name do
-    name { "tag-#{SecureRandom.hex(4)}" }
+    language_code { 'ja' }
+    script_code { 'Jpan' }
+    primary_flg { true }
+    auto_generated { false }
+    sequence(:name) { |number| "tag-#{ SecureRandom.hex(4) }-#{ number }" }
+
+    trait :alias do
+      primary_flg { false }
+    end
   end
 end

backend/spec/factories/tags.rb

@@ -1,21 +1,40 @@
 FactoryBot.define do
   factory :tag do
     transient do
-      name { nil }
+      primary_name { nil }
+      primary_tag_name do
+        attributes = primary_name.nil? ? { } : { name: primary_name }
+        build(:tag_name, **attributes)
+      end
     end
 
     category { :general }
     post_count { 0 }
-    association :tag_name
 
     after(:build) do |tag, evaluator|
-      tag.name = evaluator.name if evaluator.name.present?
+      evaluator.primary_tag_name.primary_flg = true
+      tag.tag_names.target << evaluator.primary_tag_name
     end
 
-    trait :nico do
-      category { :nico }
-      transient do
-        name { "nico:#{ SecureRandom.hex(4) }" }
+    before(:create) do |tag, evaluator|
+      evaluator.primary_tag_name.save!
+      # Compatibility write only; ownership is established through tag_id below.
+      tag.tag_name_id = evaluator.primary_tag_name.id
+    end
+
+    after(:create) do |tag, evaluator|
+      evaluator.primary_tag_name.update!(tag:, primary_flg: true)
+
+      Locale.where(deprecated_at: nil).order(:language_code, :created_at, :script_code).to_a
+          .uniq(&:language_code).each do |locale|
+        next if tag.tag_names.exists?(language_code: locale.language_code,
+                                      primary_flg: true)
+
+        create(:tag_name,
+            tag:, language_code: locale.language_code,
+            script_code: locale.script_code,
+            name: TagName.generate_name(locale, tag, evaluator.primary_tag_name),
+            primary_flg: true, auto_generated: true)
       end
     end
   end

backend/spec/models/external_tag_spec.rb

@@ -0,0 +1,38 @@
+require 'rails_helper'
+
+RSpec.describe ExternalTag, type: :model do
+  it 'preserves names without internal tag sanitisation or TagName records' do
+    external = nil
+
+    expect {
+      external = described_class.create!(platform: :nico, name: 'raw tag[]')
+    }.not_to change(TagName, :count)
+
+    expect(external.reload.name).to eq('raw tag[]')
+  end
+
+  it 'deletes post associations without deleting posts or version history' do
+    external = create(:external_tag)
+    post = create(:post)
+    PostExternalTag.create!(post:, external_tag: external)
+    version = NicoTagVersionRecorder.record!(
+        external_tag: external, event_type: :create, created_by_user: nil)
+
+    external.destroy!
+
+    expect(PostExternalTag.where(external_tag_id: external.id)).to be_empty
+    expect(post.reload.external_tags).to be_empty
+    expect(version.reload.tag_id).to eq(external.id)
+  end
+
+  it 'deletes external links without deleting linked internal tags' do
+    external = create(:external_tag)
+    tag = create(:tag)
+    NicoTagRelation.create!(nico_tag: external, tag:)
+
+    external.destroy!
+
+    expect(NicoTagRelation.where(nico_tag_id: external.id)).to be_empty
+    expect(Tag.exists?(tag.id)).to be(true)
+  end
+end

backend/spec/models/language_spec.rb

@@ -0,0 +1,32 @@
+require 'rails_helper'
+
+RSpec.describe Language, type: :model do
+  it 'accepts Nipponese as the current supported language' do
+    expect(described_class.find('ja')).to be_valid
+    expect(described_class.where(deprecated_at: nil).pluck(:code)).to eq(['ja'])
+  end
+
+  it 'accepts English when multilingual support is enabled' do
+    pending '日本語以外の Language 有効化は別課題で実装する'
+    expect { described_class.create!(code: 'en', name: 'English') }
+        .to change(described_class, :count).by(1)
+  end
+
+  it 'rejects an unsupported language code' do
+    expect {
+      described_class.create!(code: 'xx', name: 'Unsupported')
+    }.to raise_error { |error|
+      expect(error).to be_a(ArgumentError).or be_a(ActiveRecord::RecordInvalid)
+    }
+  end
+
+  ['en', 'fr'].each do |code|
+    it "does not register #{ code } as a currently supported language" do
+      expect {
+        described_class.create!(code:, name: 'Unsupported')
+      }.to raise_error { |error|
+        expect(error).to be_a(ArgumentError).or be_a(ActiveRecord::RecordInvalid)
+      }
+    end
+  end
+end

backend/spec/models/locale_spec.rb

@@ -0,0 +1,129 @@
+require 'rails_helper'
+
+RSpec.describe Locale, type: :model do
+  include_context 'English locale'
+
+  def create_english_locale!
+    prepare_english_reference!
+    described_class.create!(code: 'en', language_code: 'en',
+                            script_code: 'Latn', region_code: 826,
+                            variants: '', name: 'English')
+  end
+
+  it 'keeps the active Nipponese locale consistent with its identity tuple' do
+    expect(described_class.where(deprecated_at: nil).pluck(:code)).to eq(['ja'])
+    expect(described_class.nipponese).to have_attributes(
+        code: 'ja', language_code: 'ja', script_code: 'Jpan',
+        region_code: 392, variants: '')
+  end
+
+  it 'rejects a duplicate locale identity tuple at the database boundary' do
+    expect {
+      described_class.insert_all!([{ code: 'ja-duplicate', language_code: 'ja',
+                                    script_code: 'Jpan', region_code: 392,
+                                    variants: '', name: '日本語',
+                                    created_at: Time.current }])
+    }.to raise_error(ActiveRecord::RecordNotUnique)
+  end
+
+  it 'generates a primary name for every existing tag using the name generator' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    first = create(:tag, primary_name: 'first_existing_tag')
+    second = create(:tag, primary_name: 'second_existing_tag')
+    allow(TagName).to receive(:generate_name).and_call_original
+    allow(TagName).to receive(:generate_name)
+        .with(kind_of(described_class), first, primary_tag_name_for(first, 'ja'))
+        .and_return('name_from_generator')
+
+    locale = create_english_locale!
+
+    expect(TagName).to have_received(:generate_name)
+        .with(locale, first, primary_tag_name_for(first, 'ja'))
+    expect(TagName).to have_received(:generate_name)
+        .with(locale, second, primary_tag_name_for(second, 'ja'))
+    expect(first.tag_names.find_by!(language_code: 'en', primary_flg: true))
+        .to have_attributes(name: 'name_from_generator', tag_id: first.id,
+                            language_code: 'en', script_code: 'Latn',
+                            primary_flg: true, auto_generated: true)
+    expect(second.tag_names.find_by!(language_code: 'en', primary_flg: true))
+        .to have_attributes(tag_id: second.id, language_code: 'en',
+                            script_code: 'Latn', primary_flg: true,
+                            auto_generated: true)
+    expect(TagName.where(language_code: 'en', primary_flg: true,
+                         tag_id: [first.id, second.id]).count).to eq(2)
+  end
+
+  it 'does not duplicate an existing primary name in the new language' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    prepare_english_reference!
+    tag = create(:tag, primary_name: 'already_named')
+    existing = create(:tag_name, name: 'existing_english', tag:,
+                                 language_code: 'en', script_code: 'Latn')
+
+    create_english_locale!
+
+    expect(TagName.where(tag_id: tag.id, language_code: 'en', primary_flg: true))
+        .to contain_exactly(existing)
+    expect(existing.reload).to have_attributes(
+        tag_id: tag.id, language_code: 'en', script_code: 'Latn',
+        primary_flg: true, auto_generated: false)
+  end
+
+  it 'creates a primary name when the language has only an alias' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    prepare_english_reference!
+    tag = create(:tag, primary_name: 'alias_only_tag')
+    alias_name = create(:tag_name, :alias, name: 'alias_en',
+                                          tag:,
+                                          language_code: 'en', script_code: 'Latn')
+
+    create_english_locale!
+
+    expect(alias_name.reload).to have_attributes(
+        tag_id: tag.id,
+        language_code: 'en', script_code: 'Latn', primary_flg: false)
+    generated = TagName.find_by!(tag_id: tag.id, language_code: 'en', primary_flg: true)
+    expect(generated).to have_attributes(tag_id: tag.id, language_code: 'en',
+                                         script_code: 'Latn', primary_flg: true,
+                                         auto_generated: true)
+    expect(TagName.where(tag_id: tag.id, language_code: 'en', primary_flg: true).count).to eq(1)
+  end
+
+  it 'rolls back the locale and all generated names when backfill fails' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    prepare_english_reference!
+    first = create(:tag, primary_name: 'atomic_first')
+    second = create(:tag, primary_name: 'atomic_second')
+    allow(TagName).to receive(:generate_name).and_call_original
+    allow(TagName).to receive(:generate_name)
+        .with(kind_of(described_class), second, primary_tag_name_for(second, 'ja'))
+        .and_raise('backfill failed')
+
+    expect { create_english_locale! }.to raise_error('backfill failed')
+
+    expect(described_class.exists?(code: 'en')).to be(false)
+    expect(TagName.where(language_code: 'en', tag_id: [first.id, second.id])).to be_empty
+  end
+
+  it 'accepts a stable locale code outside the historical enum values' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    prepare_english_reference!
+
+    locale = described_class.create!(
+        code: 'en-x-rspec', language_code: 'en',
+        script_code: 'Latn', region_code: 826,
+        variants: 'x-rspec', name: 'English')
+
+    expect(locale.reload).to have_attributes(
+        code: 'en-x-rspec', language_code: 'en', script_code: 'Latn',
+        region_code: 826, variants: 'x-rspec')
+  end
+
+  it 'registers the future British English locale tuple' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+
+    expect(locale).to have_attributes(code: 'en', language_code: 'en',
+                                    script_code: 'Latn', region_code: 826,
+                                    variants: '')
+  end
+end

backend/spec/models/material_export_item_spec.rb

@@ -2,7 +2,7 @@ require 'rails_helper'
 
 RSpec.describe MaterialExportItem, type: :model do
   let(:user) { create(:user, :member) }
-  let(:tag) { Tag.create!(tag_name: TagName.create!(name: 'export_item'), category: :material) }
+  let(:tag) { create(:tag, primary_name: 'export_item', category: :material) }
   let(:material) do
     Material.create!(tag:, url: 'https://example.com/material',
                      created_by_user: user, updated_by_user: user)

backend/spec/models/nico_tag_relation_spec.rb

@@ -0,0 +1,27 @@
+require 'rails_helper'
+
+RSpec.describe NicoTagRelation, type: :model do
+  it 'does not constrain the ExternalTag association to the nico platform' do
+    external_tag = create(:external_tag)
+    tag = create(:tag)
+    allow(external_tag).to receive(:platform).and_return('registered_external')
+    allow(external_tag).to receive(:nico?).and_return(false)
+
+    expect {
+      described_class.create!(nico_tag: external_tag, tag:)
+    }.to change(described_class, :count).by(1)
+    expect(tag.linked_nico_tags).to contain_exactly(external_tag)
+  end
+
+  it 'rejects an internal Tag through the external association type' do
+    expect {
+      described_class.new(nico_tag: create(:tag), tag: create(:tag))
+    }.to raise_error(ActiveRecord::AssociationTypeMismatch)
+  end
+
+  it 'rejects an ExternalTag through the internal association type' do
+    expect {
+      described_class.new(nico_tag: create(:external_tag), tag: create(:external_tag))
+    }.to raise_error(ActiveRecord::AssociationTypeMismatch)
+  end
+end

backend/spec/models/post_external_tag_spec.rb

@@ -0,0 +1,25 @@
+require 'rails_helper'
+
+RSpec.describe PostExternalTag, type: :model do
+  it 'exposes both sides and enforces a unique post and external tag pair' do
+    post = create(:post)
+    external_tag = create(:external_tag)
+    described_class.create!(post:, external_tag:)
+
+    expect(post.external_tags).to contain_exactly(external_tag)
+    expect(external_tag.posts).to contain_exactly(post)
+    expect { described_class.create!(post:, external_tag:) }
+        .to raise_error(ActiveRecord::RecordNotUnique)
+  end
+
+  it 'removes associations when the post is deleted while retaining the external tag' do
+    post = create(:post)
+    external_tag = create(:external_tag)
+    described_class.create!(post:, external_tag:)
+
+    post.destroy!
+
+    expect(described_class.where(post_id: post.id)).to be_empty
+    expect(external_tag.reload.posts).to be_empty
+  end
+end

backend/spec/models/post_spec.rb

@@ -6,6 +6,25 @@ RSpec.describe Post, type: :model do
     PostUrlSanitisationRule.unscoped.delete_all
   end
 
+  describe '#snapshot_tags_json' do
+    it 'keeps internal snapshots and external identifiers distinct, even with the same id' do
+      post = create(:post)
+      tag = create(:tag)
+      external = create(:external_tag, id: tag.id)
+      create(:post_tag, post:, tag:)
+      create(:post_tag_section, post:, tag:, begin_ms: 2000, end_ms: nil)
+      PostExternalTag.create!(post:, external_tag: external)
+
+      expect(post.snapshot_tags_json).to eq([
+          { 'tag_id' => tag.id,
+            'version_no' => tag.version_no,
+            'name' => primary_tag_name_for(tag, 'ja').name,
+            'category' => tag.category,
+            'sections' => [{ 'begin_ms' => 2000, 'end_ms' => nil }] },
+          { 'external_tag_id' => external.id }])
+    end
+  end
+
   describe 'URL normalisation' do
     it 'normalises the HTTP URL before applying sanitisation rules' do
       PostUrlSanitisationRule.create!(

backend/spec/models/post_tag_spec.rb

@@ -1,5 +1,73 @@
+require 'rails_helper'
+
 RSpec.describe PostTag, type: :model do
+  describe 'uniqueness' do
+    it 'rejects duplicate post and tag pairs but allows either to be reused' do
+      post_tag = create(:post_tag)
+      duplicate = build(:post_tag, post: post_tag.post, tag: post_tag.tag)
+
+      expect(duplicate).not_to be_valid
+      expect(duplicate.errors.of_kind?(:post_id, :taken)).to be(true)
+      expect(build(:post_tag, post: post_tag.post, tag: create(:tag))).to be_valid
+      expect(build(:post_tag, post: create(:post), tag: post_tag.tag)).to be_valid
+    end
+
+    it 'enforces uniqueness in the database when validation is bypassed' do
+      post_tag = create(:post_tag)
+      duplicate = build(:post_tag, post: post_tag.post, tag: post_tag.tag)
+
+      expect { duplicate.save!(validate: false) }
+          .to raise_error(ActiveRecord::RecordNotUnique)
+    end
+  end
+
+  describe '#destroy!' do
+    it 'deletes only the selected pair and its sections and updates the counter' do
+      post_tag = create(:post_tag)
+      same_post = create(:post_tag, post: post_tag.post)
+      same_tag = create(:post_tag, tag: post_tag.tag)
+      sections = [post_tag, same_post, same_tag].map do |link|
+        create(:post_tag_section, post: link.post, tag: link.tag,
+                                  begin_ms: 1000, end_ms: 2000)
+      end
+
+      expect { post_tag.destroy! }.to change(described_class, :count).by(-1)
+          .and change(PostTagSection, :count).by(-1)
+          .and change { post_tag.tag.reload.post_count }.from(2).to(1)
+
+      expect(described_class.exists?(post: post_tag.post, tag: post_tag.tag)).to be(false)
+      expect(same_post.reload).to be_persisted
+      expect(same_tag.reload).to be_persisted
+      expect(PostTagSection.all).to contain_exactly(*sections.drop(1))
+      expect(post_tag.post.reload.tags).to contain_exactly(same_post.tag)
+      expect(post_tag.tag.reload.posts).to contain_exactly(same_tag.post)
+    end
+
+    it 'allows a removed tag to be added again without restoring old sections' do
+      post_tag = create(:post_tag)
+      create(:post_tag_section, post: post_tag.post, tag: post_tag.tag,
+                                begin_ms: 1000, end_ms: 2000)
+      post_tag.destroy!
+
+      replacement = create(:post_tag, post: post_tag.post, tag: post_tag.tag)
+
+      expect(replacement.reload.sections).to be_empty
+      expect(replacement.tag.reload.post_count).to eq(1)
+    end
+  end
+
   describe '#sections' do
+    it 'loads the owning post_tag from a section using both keys' do
+      post_tag = create(:post_tag)
+      create(:post_tag, post: post_tag.post)
+      create(:post_tag, tag: post_tag.tag)
+      section = create(:post_tag_section, post: post_tag.post,
+                                         tag: post_tag.tag,
+                                         begin_ms: 1000, end_ms: 2000)
+
+      expect(section.reload.post_tag).to eq(post_tag)
+    end
+
     it 'loads sections by post_id and tag_id' do
       post_tag = create(:post_tag)
       section = create(:post_tag_section,
@@ -12,18 +80,25 @@ RSpec.describe PostTag, type: :model do
     end
 
     it 'does not load sections for another tag on the same post' do
-      post = create(:post)
-      tag = create(:tag)
+      post_tag = create(:post_tag)
+      post = post_tag.post
       other_tag = create(:tag)
 
-      post_tag = create(:post_tag, post:, tag:)
+      own_section = create(:post_tag_section,
+                           post:,
+                           tag: post_tag.tag,
+                           begin_ms: 1000,
+                           end_ms: 2000)
+
+      create(:post_tag, post:, tag: other_tag)
+
       create(:post_tag_section,
              post:,
              tag: other_tag,
              begin_ms: 1000,
              end_ms: 2000)
 
-      expect(post_tag.sections).to be_empty
+      expect(post_tag.reload.sections).to contain_exactly(own_section)
     end
 
     it 'allows open-ended sections' do

backend/spec/models/post_version_spec.rb

@@ -1,8 +1,8 @@
 require 'rails_helper'
 
 RSpec.describe PostVersion, type: :model do
-  let!(:tag_name) { TagName.create!(name: 'post_version_spec_tag') }
-  let!(:tag) { Tag.create!(tag_name: tag_name, category: :general) }
+  let!(:tag_name) { create(:tag_name, name: 'post_version_spec_tag') }
+  let!(:tag) { create(:tag, primary_tag_name: tag_name, category: :general) }
 
   let!(:post_record) do
     Post.create!(title: 'spec post', url: 'https://example.com/post-version-spec').tap do |post|
@@ -19,6 +19,7 @@ RSpec.describe PostVersion, type: :model do
       url: post_record.url,
       thumbnail_base: post_record.thumbnail_base,
       tags: post_record.snapshot_tag_names.join(' '),
+      tags_json: post_record.snapshot_tags_json,
       parent_post_ids: post_record.snapshot_parent_post_ids.join(' '),
       original_created_from: post_record.original_created_from,
       original_created_before: post_record.original_created_before,

backend/spec/models/script_spec.rb

@@ -0,0 +1,35 @@
+require 'rails_helper'
+
+RSpec.describe Script, type: :model do
+  include_context 'English locale'
+
+  it 'selects locales by script code, not language code' do
+    expect(described_class.find('Jpan').locales).to contain_exactly(Locale.nipponese)
+  end
+
+  it 'accepts supported script codes and rejects unsupported ones' do
+    expect(described_class.find('Jpan')).to be_valid
+    expect(described_class.where(deprecated_at: nil).pluck(:code)).to eq(['Jpan'])
+    expect {
+      described_class.create!(code: 'Zzzz', name: 'Unsupported')
+    }.to raise_error { |error|
+      expect(error).to be_a(ArgumentError).or be_a(ActiveRecord::RecordInvalid)
+    }
+  end
+
+  it 'does not register Latin as a currently supported script' do
+    expect {
+      described_class.create!(code: 'Latn', name: 'Latin')
+    }.to raise_error { |error|
+      expect(error).to be_a(ArgumentError).or be_a(ActiveRecord::RecordInvalid)
+    }
+  end
+
+  it 'selects Latin locales when multilingual support is enabled' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    locale
+
+    expect(described_class.find('Latn').locales).to contain_exactly(locale)
+    expect(described_class.find('Jpan').locales).not_to include(locale)
+  end
+end

backend/spec/models/tag_implication_spec.rb

@@ -2,8 +2,8 @@ require 'rails_helper'
 
 RSpec.describe TagImplication, type: :model do
   it 'rejects a parent tag that would create a cycle' do
-    child = create(:tag, name: 'tag_implication_cycle_child')
-    parent = create(:tag, name: 'tag_implication_cycle_parent')
+    child = create(:tag, primary_name: 'tag_implication_cycle_child')
+    parent = create(:tag, primary_name: 'tag_implication_cycle_parent')
 
     described_class.create!(tag: child, parent_tag: parent)
 
@@ -17,9 +17,9 @@ RSpec.describe TagImplication, type: :model do
   end
 
   it 'terminates even when existing data already contains a cycle' do
-    child = create(:tag, name: 'tag_implication_existing_cycle_child')
-    parent = create(:tag, name: 'tag_implication_existing_cycle_parent')
-    ancestor = create(:tag, name: 'tag_implication_existing_cycle_ancestor')
+    child = create(:tag, primary_name: 'tag_implication_existing_cycle_child')
+    parent = create(:tag, primary_name: 'tag_implication_existing_cycle_parent')
+    ancestor = create(:tag, primary_name: 'tag_implication_existing_cycle_ancestor')
 
     described_class.create!(tag: parent, parent_tag: ancestor)
     described_class.insert_all!(

backend/spec/models/tag_name_sanitisation_rule_spec.rb

@@ -31,12 +31,48 @@ RSpec.describe TagNameSanitisationRule, type: :model do
 
   describe '.apply!' do
     before do
-      described_class.create!(priority: 10, source_pattern: '_', replacement: '')
+      described_class.create!(priority: 10, source_pattern: 'foo_', replacement: 'foo')
+    end
+
+    context 'when only another language has the sanitised name' do
+      include_context 'English locale'
+
+      it 'keeps both names when sanitisation produces a cross-language match' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        nipponese = create(:tag_name, name: 'foobar')
+        english = create(:tag_name, name: 'temporary',
+                                   language_code: 'en', script_code: 'Latn')
+        english.update_columns(name: 'foo_bar')
+
+        expect { described_class.apply! }.not_to change(TagName, :count)
+
+        expect(english.reload).to have_attributes(name: 'foobar', language_code: 'en')
+        expect(nipponese.reload).to have_attributes(name: 'foobar', language_code: 'ja')
+      end
+
+      it 'renames without merging tags or deleting either language identity' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        nipponese = create(:tag, primary_name: 'foobar')
+        english_name = create(:tag_name, name: 'temporary',
+                                        language_code: 'en', script_code: 'Latn')
+        english = create(:tag, primary_tag_name: english_name)
+        english_name.update_columns(name: 'foo_bar')
+
+        described_class.apply!
+
+        expect(english_name.reload).to have_attributes(
+            name: 'foobar', language_code: 'en', tag_id: english.id)
+        expect(primary_tag_name_for(nipponese.reload, 'ja')).to have_attributes(
+            name: 'foobar', language_code: 'ja', tag_id: nipponese.id)
+        expect(primary_tag_name_for(english.reload, 'en')).to eq(english_name)
+      end
     end
 
     context 'when no conflicting tag_name exists' do
       let!(:tag_name) do
-        TagName.create!(name: 'tmp').tap do |tn|
+        create(:tag_name, name: 'tmp').tap do |tn|
           tn.update_columns(name: 'foo_bar', updated_at: Time.current)
         end
       end
@@ -47,44 +83,72 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       end
     end
 
-    context 'when a conflicting canonical tag_name exists' do
-      let!(:existing) { TagName.create!(name: 'foobar') }
+    context 'when a conflicting primary tag name exists' do
+      let!(:existing) { create(:tag_name, name: 'foobar') }
       let!(:source) do
-        TagName.create!(name: 'tmp').tap do |tn|
+        create(:tag_name, name: 'tmp').tap do |tn|
           tn.update_columns(name: 'foo_bar', updated_at: Time.current)
         end
       end
 
       it 'deletes the source tag_name' do
         described_class.apply!
-        expect(TagName.exists?(source.id)).to be(false)
+        expect(TagName.unscoped.exists?(source.id)).to be(false)
         expect(existing.reload.name).to eq('foobar')
       end
     end
 
     context 'when the source tag_name has a tag and the existing one has no tag' do
-      let!(:existing) { TagName.create!(name: 'foobar') }
-      let!(:source_tag) { create(:tag, name: 'tmp', category: :general) }
-      let!(:source_tag_name_id) { source_tag.tag_name_id }
+      let!(:existing) { create(:tag_name, name: 'foobar') }
+      let!(:source_tag) { create(:tag, primary_name: 'tmp', category: :general) }
+      let!(:source_tag_name_id) { primary_tag_name_for(source_tag, 'ja').id }
 
       before do
-        source_tag.tag_name.update_columns(name: 'foo_bar', updated_at: Time.current)
+        primary_tag_name_for(source_tag, 'ja').update_columns(
+            name: 'foo_bar', updated_at: Time.current)
       end
 
       it 'moves the tag to the existing tag_name' do
         described_class.apply!
-        expected_tag_name_id = existing.canonical_id || existing.id
-        expect(source_tag.reload.tag_name_id).to eq(expected_tag_name_id)
-        expect(TagName.exists?(source_tag_name_id)).to be(false)
+        expect(existing.reload).to have_attributes(
+            tag_id: source_tag.id, language_code: 'ja', primary_flg: true)
+        expect(primary_tag_name_for(source_tag, 'ja')).to eq(existing)
+        expect(primary_tag_name_for(source_tag.reload, 'ja')).to eq(existing)
+        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
+      end
+    end
+
+    context 'when the sanitised name is an alias of an existing tag' do
+      let!(:existing_tag) { create(:tag) }
+      let!(:existing_primary) { primary_tag_name_for(existing_tag, 'ja') }
+      let!(:alias_name) do
+        create(:tag_name, :alias, name: 'foobar', tag: existing_tag)
+      end
+      let!(:source) do
+        create(:tag_name, name: 'tmp').tap do |tn|
+          tn.update_columns(name: 'foo_bar', updated_at: Time.current)
+        end
+      end
+
+      it 'deletes only the source and preserves the alias and its owning tag' do
+        described_class.apply!
+
+        expect(TagName.unscoped.exists?(source.id)).to be(false)
+        expect(alias_name.reload).to have_attributes(
+            tag_id: existing_tag.id, language_code: 'ja', primary_flg: false)
+        expect(TagName.find_by!(tag_id: existing_tag.id,
+                                language_code: 'ja', primary_flg: true))
+            .to eq(existing_primary)
+        expect(Tag.find(existing_tag.id)).to eq(existing_tag)
       end
     end
 
     context 'when both source and existing tag_names have tags' do
-      let!(:existing_tn) { TagName.create!(name: 'foobar') }
-      let!(:existing_tag) { Tag.create!(tag_name: existing_tn, category: :general) }
+      let!(:existing_tn) { create(:tag_name, name: 'foobar') }
+      let!(:existing_tag) { create(:tag, primary_tag_name: existing_tn, category: :general) }
 
-      let!(:source_tn) { TagName.create!(name: 'tmp') }
-      let!(:source_tag) { Tag.create!(tag_name: source_tn, category: :general) }
+      let!(:source_tn) { create(:tag_name, name: 'tmp') }
+      let!(:source_tag) { create(:tag, primary_tag_name: source_tn, category: :general) }
       let!(:source_tag_name_id) { source_tn.id }
 
       before do
@@ -92,13 +156,15 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       end
 
       it 'merges the source tag into the existing tag and deletes the source tag_name' do
-        expect(TagName.find_by(name: 'foobar')&.tag&.id).to eq(existing_tag.id)
-        expect(TagName.find_by(name: 'foo_bar')&.tag&.id).to eq(source_tag.id)
+        post = create(:post)
+        PostTag.create!(post:, tag: source_tag)
 
         described_class.apply!
 
-        expect(Tag.exists?(source_tag.id)).to be(false)
-        expect(TagName.exists?(source_tag.tag_name_id)).to be(false)
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
+        expect(post.reload.tags).to contain_exactly(existing_tag)
+        expect(primary_tag_name_for(existing_tag.reload, 'ja').name).to eq('foobar')
       end
     end
   end

backend/spec/models/tag_name_spec.rb

@@ -0,0 +1,171 @@
+require 'rails_helper'
+
+RSpec.describe TagName, type: :model do
+  include_context 'English locale'
+
+  it 'allows the same name in different languages' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    locale
+    create(:tag_name, name: 'shared_name')
+    english = build(:tag_name, name: 'shared_name',
+                              language_code: 'en', script_code: 'Latn')
+
+    expect(english).to be_valid
+    expect { english.save! }.to change(described_class, :count).by(1)
+  end
+
+  it 'rejects a duplicate name within the same language' do
+    create(:tag_name, name: 'shared_name')
+    duplicate = build(:tag_name, name: 'shared_name')
+
+    expect(duplicate).to be_invalid
+    expect(duplicate.errors.of_kind?(:name, :taken)).to be(true)
+  end
+
+  it 'creates Nipponese factory names without requiring a tag' do
+    name = create(:tag_name)
+
+    expect(name.reload).to have_attributes(
+        language_code: 'ja', script_code: 'Jpan', primary_flg: true,
+        auto_generated: false, tag_id: nil)
+  end
+
+  it 'defaults ordinary persisted human names to confirmed provenance' do
+    name = described_class.create!(name: 'ordinary_human_name', language_code: 'ja',
+                                   script_code: 'Jpan', primary_flg: true)
+
+    expect(name.reload.auto_generated).to be(false)
+  end
+
+  it 'persists both sides of the representative tag factory association' do
+    name = create(:tag_name)
+    tag = create(:tag, primary_tag_name: name)
+
+    expect(name.reload).to have_attributes(
+        tag_id: tag.id, language_code: 'ja', script_code: 'Jpan', primary_flg: true)
+    expect(name.tag).to eq(tag)
+    expect(described_class.find_by!(tag_id: tag.id, language_code: 'ja', primary_flg: true))
+        .to eq(name)
+    expect(tag.reload.tag_name_id).to eq(name.id)
+  end
+
+  it 'creates a complete ordinary tag factory under the active Nipponese language' do
+    tag = create(:tag, primary_name: 'factory_multilingual')
+
+    Locale.where(deprecated_at: nil).distinct.pluck(:language_code).each do |language_code|
+      expect(TagName.where(tag:, language_code:, primary_flg: true).count).to eq(1)
+    end
+    expect(TagName.where(tag:, language_code: 'ja', primary_flg: true))
+        .to contain_exactly(have_attributes(auto_generated: false))
+  end
+
+  it 'completes an ordinary tag factory under future active languages' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    locale
+    tag = create(:tag, primary_name: 'future_factory')
+
+    expect(TagName.where(tag:, language_code: 'en', primary_flg: true))
+        .to contain_exactly(have_attributes(auto_generated: true))
+  end
+
+  it 'builds a primary name without persisting the tag or its name' do
+    tag = nil
+
+    expect {
+      tag = build(:tag, primary_name: 'built_primary')
+    }.to change(Tag, :count).by(0).and change(described_class, :count).by(0)
+
+    expect(tag).to be_new_record
+    expect(tag.tag_names.target).to contain_exactly(have_attributes(
+        name: 'built_primary', language_code: 'ja', script_code: 'Jpan',
+        primary_flg: true))
+  end
+
+  it 'persists an alias owned by the same tag as its primary name' do
+    primary_name = create(:tag_name)
+    tag = create(:tag, primary_tag_name: primary_name)
+    alias_name = create(:tag_name, :alias, name: 'valid_alias', tag:)
+
+    expect(alias_name.reload).to have_attributes(
+        tag_id: tag.id,
+        primary_flg: false, language_code: 'ja')
+    primary = described_class.find_by!(tag_id: alias_name.tag_id,
+                                       language_code: alias_name.language_code,
+                                       primary_flg: true)
+    expect(primary).to eq(primary_name)
+  end
+
+  describe '.canonicalise' do
+    it 'leaves detached aliases unchanged' do
+      create(:tag_name, :alias, name: 'detached_alias')
+
+      expect(described_class.canonicalise(Locale.nipponese, ['detached_alias']))
+          .to eq(['detached_alias'])
+    end
+
+    it 'does not resolve a detached alias through another detached primary' do
+      create(:tag_name, :alias, name: 'detached_alias')
+      create(:tag_name, name: 'unrelated_detached_primary')
+
+      expect(described_class.canonicalise(Locale.nipponese, ['detached_alias']))
+          .to eq(['detached_alias'])
+    end
+
+    it 'resolves the primary name of the alias language on the same tag' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      tag = create(:tag, primary_name: '日本語正本')
+      english_primary = primary_tag_name_for(tag, 'en')
+      english_primary.update!(name: 'english_primary', auto_generated: false)
+      english_alias = create(:tag_name, :alias, tag:, name: 'english_alias',
+                                                 language_code: 'en', script_code: 'Latn')
+      representative_id = tag.tag_name_id
+
+      primary = described_class.find_by!(tag_id: english_alias.tag_id,
+                                         language_code: english_alias.language_code,
+                                         primary_flg: true)
+
+      expect(primary).to eq(english_primary)
+      expect(described_class.canonicalise(locale, [english_alias.name]))
+          .to eq([english_primary.name])
+      expect(tag.reload.tag_name_id).to eq(representative_id)
+    end
+
+    it 'resolves only aliases in the requested language' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      nipponese = create(:tag, primary_name: 'nipponese_canonical')
+      english_name = create(:tag_name, name: 'english_canonical',
+                                      language_code: 'en', script_code: 'Latn')
+      english = create(:tag, primary_tag_name: english_name)
+      nipponese_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                  tag: nipponese)
+      english_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                tag: english,
+                                                language_code: 'en', script_code: 'Latn')
+
+      expect(nipponese_alias.reload).to have_attributes(
+          tag_id: nipponese.id,
+          primary_flg: false, language_code: 'ja')
+      expect(english_alias.reload).to have_attributes(
+          tag_id: english.id,
+          primary_flg: false, language_code: 'en')
+      expect(described_class.canonicalise(locale, ['shared_alias']))
+          .to eq(['english_canonical'])
+      expect(described_class.canonicalise(Locale.nipponese, ['shared_alias']))
+          .to eq(['nipponese_canonical'])
+    end
+  end
+
+  it 'rejects the generated-name prefix in human input' do
+    human_name = build(:tag_name, name: 'Tag_#999', auto_generated: false)
+
+    expect(human_name).to be_invalid
+  end
+
+  it 'allows the generated-name prefix for system-created names' do
+    generated_name = build(:tag_name, name: 'Tag_#1000', auto_generated: true)
+
+    expect { generated_name.save! }.to change(described_class, :count).by(1)
+  end
+end

backend/spec/models/tag_spec.rb

@@ -1,129 +1,185 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
+  describe 'external tag separation' do
+    ['nico:reserved', 'NiCo:reserved'].each do |name|
+      it "rejects the reserved prefix #{ name } for internal tags" do
+        tag = build(:tag, primary_name: name)
+
+        expect(tag).to be_invalid
+        expect(tag.errors[:name]).to be_present
+        expect {
+          described_class.normalise_tags!(Locale.nipponese, [name])
+        }.to raise_error(Tag::NicoTagNormalisationError)
+      end
+    end
+
+    it 'finds external links by the internal tag id even when ids differ' do
+      tag = create(:tag)
+      external = create(:external_tag, id: tag.id + 10_000)
+      # The migration retains existing links without running model validation.
+      NicoTagRelation.insert_all!([{ tag_id: tag.id, nico_tag_id: external.id }])
+
+      expect(tag.linked_nico_tags).to contain_exactly(external)
+    end
+  end
+
   describe '.normalise_tags!' do
+    include_context 'English locale'
+
+    it 'canonicalises aliases in the supplied language only' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      prepare_english_reference!
+      nipponese = create(:tag, primary_name: 'nipponese_canonical')
+      english_name = create(:tag_name, name: 'english_canonical',
+                                      language_code: 'en', script_code: 'Latn')
+      english = create(:tag, primary_tag_name: english_name)
+      primary_tag_name_for(english, 'ja').update!(
+          name: 'english_in_nipponese', auto_generated: false)
+      english_locale = locale
+      nipponese_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                  tag: nipponese)
+      english_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                tag: english,
+                                                language_code: 'en', script_code: 'Latn')
+
+      expect(nipponese_alias.reload).to have_attributes(
+          tag_id: nipponese.id,
+          primary_flg: false, language_code: 'ja')
+      expect(english_alias.reload).to have_attributes(
+          tag_id: english.id,
+          primary_flg: false, language_code: 'en')
+      expect(described_class.normalise_tags!(
+          english_locale, ['shared_alias'],
+          with_tagme: false, with_no_deerjikist: false)).to eq([english])
+      expect(described_class.normalise_tags!(
+          Locale.nipponese, ['shared_alias'],
+          with_tagme: false, with_no_deerjikist: false)).to eq([nipponese])
+    end
+
     it 'rejects deprecated tags when deny_deprecated is enabled' do
-      tag_name = TagName.create!(name: 'normalise deprecated tag')
-      deprecated_tag = Tag.create!(
-        tag_name:,
-        category: :general,
-        deprecated_at: 1.day.from_now
-      )
+      tag_name = create(:tag_name, name: 'normalise deprecated tag')
+      deprecated_tag = create(:tag,
+          primary_tag_name: tag_name,
+          category: :general,
+          deprecated_at: 1.day.from_now)
 
       expect {
-        described_class.normalise_tags!(
-          [deprecated_tag.name],
-          deny_deprecated: true
-        )
+        described_class.normalise_tags!(Locale.nipponese,
+            [primary_tag_name_for(deprecated_tag, 'ja').name],
+            deny_deprecated: true)
       }.to raise_error(Tag::DeprecatedTagNormalisationError) { |error|
-        expect(error.tag_names).to eq([deprecated_tag.name])
+        expect(error.tag_names).to eq([primary_tag_name_for(deprecated_tag, 'ja').name])
       }
     end
 
     it 'rejects invalid section literals instead of treating them as zero' do
       expect {
-        described_class.normalise_tags!(
-          ['normalise_invalid_section[1:aa-2:00]'],
-          with_sections: true
-        )
+        described_class.normalise_tags!(Locale.nipponese,
+            ['normalise_invalid_section[1:aa-2:00]'],
+            with_sections: true)
       }.to raise_error(Tag::SectionLiteralParseError)
     end
 
     it 'parses open-ended section literals' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[1:00-]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[1:00-]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
     end
 
     it 'parses omitted begin as zero' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[-1:00]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[-1:00]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, 60_000]])
     end
 
     it 'treats fully open section literals as plain tags' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[-]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[-]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections)[tag.id]).to be_nil
     end
 
     it 'treats [0:00-] as a plain tag' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[0:00-]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[0:00-]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections)[tag.id]).to be_nil
     end
 
     it 'expands zero-width sections to one millisecond' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[1:00-1:00]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[1:00-1:00]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 60_001]])
     end
 
     it 'swaps reversed section boundaries' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[2:00-1:00]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[2:00-1:00]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 120_000]])
     end
 
     it 'merges open-ended sections over later bounded sections' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[1:00-][2:00-3:00]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[1:00-][2:00-3:00]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
     end
 
     it 'merges adjacent bounded and open-ended sections' do
-      result = described_class.normalise_tags!(
-        ['伊地知ニジカ[1:00-3:00][3:00-]'],
-        with_sections: true
-      )
+      result = described_class.normalise_tags!(Locale.nipponese,
+          ['伊地知ニジカ[1:00-3:00][3:00-]'],
+          with_sections: true)
 
-      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      tag = result.fetch(:tags).find do |candidate|
+        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
+      end
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
     end
   end
 
   describe '.expand_parent_tags' do
     it 'expands through multiple deprecated parents to an active ancestor' do
-      child = create(:tag, name: 'expand_child')
-      deprecated_parent = create(
-        :tag,
-        name: 'expand_deprecated_parent',
-        deprecated_at: Time.current
-      )
-      deprecated_grandparent = create(
-        :tag,
-        name: 'expand_deprecated_grandparent',
-        deprecated_at: Time.current
-      )
-      active_ancestor = create(:tag, name: 'expand_active_ancestor')
+      child = create(:tag, primary_name: 'expand_child')
+      deprecated_parent = create(:tag,
+          primary_name: 'expand_deprecated_parent',
+          deprecated_at: Time.current)
+      deprecated_grandparent = create(:tag,
+          primary_name: 'expand_deprecated_grandparent',
+          deprecated_at: Time.current)
+      active_ancestor = create(:tag, primary_name: 'expand_active_ancestor')
       TagImplication.create!(tag: child, parent_tag: deprecated_parent)
       TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
       TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_ancestor)
@@ -140,8 +196,8 @@ RSpec.describe Tag, type: :model do
     end
 
     it 'terminates when implications contain a cycle' do
-      first = create(:tag, name: 'expand_cycle_first')
-      second = create(:tag, name: 'expand_cycle_second')
+      first = create(:tag, primary_name: 'expand_cycle_first')
+      second = create(:tag, primary_name: 'expand_cycle_second')
       TagImplication.create!(tag: first, parent_tag: second)
       now = Time.current
       TagImplication.insert_all!(
@@ -159,45 +215,282 @@ RSpec.describe Tag, type: :model do
     end
   end
 
-  describe 'deprecated validation' do
-    it 'rejects deprecated nico tags' do
-      tag = build(
-        :tag,
-        name: 'nico:deprecated_validation',
-        category: :nico,
-        deprecated_at: Time.current
-      )
+  describe '.find_or_create_by_tag_name!' do
+    context 'with an explicit locale' do
+      include_context 'English locale'
 
-      expect(tag).not_to be_valid
-      expect(tag.errors[:deprecated_at]).to include('ニコタグは廃止できません．')
+      it 'creates the representative name with locale attributes and ownership' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        tag = described_class.find_or_create_by_tag_name!(
+            locale, 'english_name', category: :character)
+
+        expect(primary_tag_name_for(tag, 'en')).to have_attributes(
+            language_code: 'en', script_code: 'Latn',
+            primary_flg: true, tag_id: tag.id)
+        expect(tag.category).to eq('character')
+      end
+
+      it 'uses the English primary as the source for a generated Nipponese name' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        allow(TagName).to receive(:generate_name).and_return('generated_nipponese')
+
+        tag = described_class.find_or_create_by_tag_name!(
+            locale, 'english_origin', category: :general)
+
+        expect(TagName.where(tag:, language_code: 'en', primary_flg: true))
+            .to contain_exactly(have_attributes(
+                name: 'english_origin', auto_generated: false))
+        expect(TagName.where(tag:, language_code: 'ja', primary_flg: true))
+            .to contain_exactly(have_attributes(
+                name: 'generated_nipponese', auto_generated: true))
+        source_tag_name = TagName.find_by!(tag:, language_code: 'en', primary_flg: true)
+        expect(TagName).to have_received(:generate_name)
+            .with(Locale.nipponese, tag, source_tag_name)
+      end
+
+      it 'gives a new tag one primary name for every active language' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        tag = described_class.find_or_create_by_tag_name!(
+            Locale.nipponese, 'new_multilingual_tag', category: :general)
+
+        expect(TagName.where(tag:, language_code: 'ja', primary_flg: true).count).to eq(1)
+        expect(TagName.where(tag:, language_code: 'en', primary_flg: true).count).to eq(1)
+      end
+
+      it 'creates one primary per language when multiple locales use English' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        described_class.find_or_create_by_tag_name!(
+            locale, 'before_second_english_locale', category: :general)
+        Locale.create!(code: 'en-x-rspec', language_code: 'en',
+                       script_code: 'Latn', region_code: 826,
+                       variants: 'x-rspec', name: 'English')
+
+        tag = described_class.find_or_create_by_tag_name!(
+            locale, 'one_english_primary', category: :general)
+
+        expect(TagName.where(tag:, language_code: 'en', primary_flg: true).count).to eq(1)
+        expect(TagName.where(tag:, language_code: 'ja', primary_flg: true).count).to eq(1)
+      end
+
+      it 'rolls back a new tag and requested name if name generation fails' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        original_tag_count = described_class.count
+        allow(TagName).to receive(:generate_name).and_raise('generation failed')
+
+        expect {
+          described_class.find_or_create_by_tag_name!(
+              locale, 'atomic_english_name', category: :general)
+        }.to raise_error('generation failed')
+
+        expect(described_class.count).to eq(original_tag_count)
+        expect(TagName.where(language_code: 'en', name: 'atomic_english_name')).to be_empty
+        expect(described_class.joins(:tag_names)
+            .where(tag_names: { name: 'atomic_english_name' })).to be_empty
+      end
+
+      it 'keeps a detached requested name detached if generation fails' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        detached = create(:tag_name, :alias, name: 'atomic_detached',
+                                           language_code: 'en', script_code: 'Latn')
+        original_tag_count = described_class.count
+        allow(TagName).to receive(:generate_name).and_raise('generation failed')
+
+        expect {
+          described_class.find_or_create_by_tag_name!(
+              locale, detached.name, category: :general)
+        }.to raise_error('generation failed')
+
+        expect(described_class.count).to eq(original_tag_count)
+        expect(detached.reload).to have_attributes(tag_id: nil, primary_flg: false)
+      end
+
+      it 'promotes a detached alias into the requested primary name' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        detached = create(:tag_name, :alias, name: 'detached_english',
+                                           language_code: 'en', script_code: 'Latn')
+
+        tag = described_class.find_or_create_by_tag_name!(
+            locale, detached.name, category: :general)
+
+        expect(detached.reload).to have_attributes(
+            tag_id: tag.id, primary_flg: true, canonical_id: nil,
+            auto_generated: false)
+        expect(TagName.where(tag:, language_code: 'en', primary_flg: true))
+            .to contain_exactly(detached)
+      end
+
+      it 'creates separate tag identities for the same name in different languages' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        nipponese = described_class.find_or_create_by_tag_name!(
+            Locale.nipponese, 'same_name', category: :general)
+        english = described_class.find_or_create_by_tag_name!(
+            locale, 'same_name', category: :character)
+
+        expect(english).not_to eq(nipponese)
+        expect(primary_tag_name_for(english, 'en')).to have_attributes(
+            name: 'same_name', tag_id: english.id, language_code: 'en', primary_flg: true)
+        expect(primary_tag_name_for(nipponese, 'ja')).to have_attributes(
+            name: 'same_name', tag_id: nipponese.id, language_code: 'ja', primary_flg: true)
+        expect(described_class.find_or_create_by_tag_name!(
+            locale, 'same_name', category: :general)).to eq(english)
+        expect(described_class.find_or_create_by_tag_name!(
+            Locale.nipponese, 'same_name', category: :general)).to eq(nipponese)
+      end
+
+      it 'preserves the V1 representative when looking up another primary language' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        tag = create(:tag, primary_name: '日本語代表名')
+        representative_id = tag.tag_name_id
+        english = primary_tag_name_for(tag, 'en')
+        english.update!(name: 'english_primary', auto_generated: false)
+
+        found = described_class.find_or_create_by_tag_name!(
+            locale, english.name, category: :general)
+
+        expect(found).to eq(tag)
+        expect(tag.reload.tag_name_id).to eq(representative_id)
+        expect(english.reload.tag_id).to eq(tag.id)
+      end
+
+      it 'normalises names using the supplied locale' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        tags = described_class.normalise_tags!(
+            locale, ['character:normalised_english'],
+            with_tagme: false, with_no_deerjikist: false)
+
+        expect(tags.length).to eq(1)
+        expect(primary_tag_name_for(tags.first, 'en')).to have_attributes(
+            name: 'normalised_english', language_code: 'en', script_code: 'Latn',
+            primary_flg: true, tag_id: tags.first.id)
+      end
+    end
+
+    it 'creates a tag and name with the requested category after stripping whitespace' do
+      tag = nil
+
+      expect {
+        tag = described_class.find_or_create_by_tag_name!(Locale.nipponese,
+            '  lookup_new  ', category: :character)
+      }.to change(Tag, :count).by(1).and change(TagName, :count).by(1)
+
+      expect(primary_tag_name_for(tag, 'ja').name).to eq('lookup_new')
+      expect(tag.category).to eq('character')
+      expect(TagName.where(tag:, language_code: 'ja', primary_flg: true).count).to eq(1)
+      expect(primary_tag_name_for(tag, 'ja').auto_generated).to be(false)
+    end
+
+    it 'promotes a detached Nipponese alias into a human-confirmed primary' do
+      detached = create(:tag_name, :alias, name: 'detached_nipponese')
+
+      tag = described_class.find_or_create_by_tag_name!(
+          Locale.nipponese, detached.name, category: :general)
+
+      expect(detached.reload).to have_attributes(
+          tag_id: tag.id, primary_flg: true, canonical_id: nil,
+          auto_generated: false)
+      expect(TagName.where(tag:, language_code: 'ja', primary_flg: true))
+          .to contain_exactly(detached)
+    end
+
+    it 'reuses the owning tag for an alias without changing its category' do
+      tag = create(:tag, category: :character)
+      representative_id = tag.tag_name_id
+      alias_name = create(:tag_name, :alias, name: 'lookup_alias', tag:)
+      expect(alias_name.reload).to have_attributes(
+          tag_id: tag.id,
+          primary_flg: false, language_code: 'ja')
+      found = nil
+
+      expect {
+        found = described_class.find_or_create_by_tag_name!(Locale.nipponese,
+            alias_name.name, category: :general)
+      }.to change(Tag, :count).by(0).and change(TagName, :count).by(0)
+
+      expect(found).to eq(tag)
+      expect(found.category).to eq('character')
+      expect(tag.reload.tag_name_id).to eq(representative_id)
+    end
+
+    it 'reuses the owning tag through another alias' do
+      tag = create(:tag)
+      primary = primary_tag_name_for(tag, 'ja')
+      alias_name = create(:tag_name, :alias, name: 'lookup_alias', tag:)
+      other_alias = create(:tag_name, :alias, name: 'lookup_other_alias', tag:)
+
+      expect([alias_name.reload, other_alias.reload]).to all(have_attributes(
+          tag_id: tag.id,
+          primary_flg: false, language_code: 'ja'))
+
+      expect {
+        found = described_class.find_or_create_by_tag_name!(Locale.nipponese,
+            alias_name.name, category: :general)
+        expect(found).to eq(tag)
+      }.to change(Tag, :count).by(0).and change(TagName, :count).by(0)
+
+      expect(primary_tag_name_for(tag.reload, 'ja')).to eq(primary)
     end
   end
 
   describe '.merge_tags!' do
     let!(:target_tag) { create(:tag, category: :general) }
     let!(:source_tag) { create(:tag, category: :general) }
-    let!(:source_tag_name) { source_tag.tag_name }
+    let!(:source_tag_name) { primary_tag_name_for(source_tag, 'ja') }
 
     let!(:post_record) do
       Post.create!(url: 'https://example.com/posts/1', title: 'test post')
     end
 
+    context 'with names in multiple languages' do
+      include_context 'English locale'
+
+      it 'keeps the target primary and moves source names as aliases' do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        english_primary = primary_tag_name_for(target_tag, 'en')
+        source_primary = primary_tag_name_for(source_tag, 'en')
+        source_alias = create(:tag_name, :alias, tag: source_tag,
+            name: 'source_english_alias', language_code: 'en', script_code: 'Latn')
+
+        expect([english_primary, source_primary]).to all(have_attributes(
+            primary_flg: true, auto_generated: true))
+
+        described_class.merge_tags!(target_tag, [source_tag])
+
+        expect(primary_tag_name_for(target_tag.reload, 'en')).to eq(english_primary)
+        expect(TagName.where(tag: target_tag, language_code: 'en', primary_flg: true))
+            .to contain_exactly(english_primary)
+        expect([source_primary.reload, source_alias.reload]).to all(have_attributes(
+            tag_id: target_tag.id, language_code: 'en', primary_flg: false))
+        expect(TagName.where(tag: target_tag, language_code: 'ja', primary_flg: true))
+            .to contain_exactly(primary_tag_name_for(target_tag, 'ja'))
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
+      end
+    end
+
     context 'when merging a simple source tag' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
-      it 'discards the source post_tag, creates an active target post_tag, discards the source tag, and aliases the source tag_name' do
+      it 'deletes the source tag, moves its post link, and keeps its name as an alias' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
-        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
+        target_link = PostTag.find_by(post: post_record, tag: target_tag)
 
-        expect(source_pt.discarded_at).to be_present
-        expect(source_pt.tag_id).to eq(source_tag.id)
-        expect(active_target).to be_present
-
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
-        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
+        expect(target_link).to be_present
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -206,39 +499,108 @@ RSpec.describe Tag, type: :model do
       let!(:target_post_tag) { PostTag.create!(post: post_record, tag: target_tag) }
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
-      it 'discards the source post_tag, keeps one active target post_tag, discards the source tag, and aliases the source tag_name' do
+      it 'deletes the source link and preserves the existing target link' do
+        create(:post_tag_section, post: post_record, tag: source_tag,
+                                  begin_ms: 1000, end_ms: 2000)
+        target_section = create(:post_tag_section, post: post_record,
+                                                   tag: target_tag,
+                                                   begin_ms: 3000, end_ms: nil)
+
         described_class.merge_tags!(target_tag, [source_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
-        active = PostTag.kept.where(post_id: post_record.id, tag_id: target_tag.id)
+        target_links = PostTag.where(post: post_record, tag: target_tag)
 
-        expect(source_pt.discarded_at).to be_present
-        expect(source_pt.tag_id).to eq(source_tag.id)
-        expect(active.count).to eq(1)
-        expect(active.first.id).to eq(target_post_tag.id)
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
+        expect(target_links).to contain_exactly(target_post_tag)
+        expect(PostTagSection.where(post: post_record, tag: source_tag)).to be_empty
+        expect(target_post_tag.reload.sections).to contain_exactly(target_section)
 
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
-        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
 
+    it 'keeps source history and records the new target alias after deleting the source' do
+      user = create_member_user!
+      source_name = primary_tag_name_for(source_tag, 'ja').name
+      source_alias = create(:tag_name, :alias, name: 'merge_alias', tag: source_tag)
+      TagVersioning.ensure_snapshot!(source_tag, created_by_user: user)
+      original_version = source_tag.tag_versions.first
+
+      described_class.merge_tags!(target_tag, [source_tag], created_by_user: user)
+
+      versions = TagVersion.where(tag_id: source_tag.id).order(:version_no)
+      expect(versions.pluck(:version_no, :event_type))
+          .to eq([[1, 'create'], [2, 'discard']])
+      expect(versions.first).to eq(original_version)
+      expect(versions.last.created_by_user).to eq(user)
+      expect(versions.last.names.fetch('ja')).to eq(
+          'name' => source_name, 'script_code' => 'Jpan',
+          'auto_generated' => false,
+          'aliases' => [{ 'name' => source_alias.name, 'script_code' => 'Jpan' }])
+      expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+
+      target_versions = target_tag.tag_versions.order(:version_no)
+      expect(target_versions.pluck(:event_type)).to eq(['create', 'update'])
+      target_aliases = target_versions.last.names.fetch('ja').fetch('aliases').pluck('name')
+      expect(target_aliases).to contain_exactly('merge_alias', source_name)
+    end
+
+    it 'deletes source relationships while preserving unrelated relationships' do
+      parent = create(:tag)
+      child = create(:tag)
+      nico_tag = create(:external_tag)
+      TagImplication.create!(tag: source_tag, parent_tag: parent)
+      TagImplication.create!(tag: child, parent_tag: source_tag)
+      kept_implication = TagImplication.create!(tag: target_tag, parent_tag: parent)
+      NicoTagRelation.create!(tag: source_tag, nico_tag:)
+      kept_relation = NicoTagRelation.create!(tag: target_tag, nico_tag:)
+      TagSimilarity.create!(tag: source_tag, target_tag:, cos: 0.5)
+      TagSimilarity.create!(tag: target_tag, target_tag: source_tag, cos: 0.5)
+      kept_similarity = TagSimilarity.create!(tag: target_tag, target_tag: parent,
+                                               cos: 0.5)
+
+      described_class.merge_tags!(target_tag, [source_tag])
+
+      expect(TagImplication.all).to contain_exactly(kept_implication)
+      expect(NicoTagRelation.all).to contain_exactly(kept_relation)
+      expect(TagSimilarity.all).to contain_exactly(kept_similarity)
+      expect(TagVersion.where(tag_id: source_tag.id).order(:version_no).last.parent_tag_ids)
+          .to eq(parent.id.to_s)
+    end
+
+    it 'preserves material history referencing the deleted source tag' do
+      source_tag.update!(category: :material)
+      target_tag.update!(category: :material)
+      material = Material.create!(tag: source_tag, url: 'https://example.com/material')
+      version = MaterialVersionRecorder.record!(
+          material:, event_type: :create, created_by_user: nil)
+      material.update!(tag: target_tag)
+
+      described_class.merge_tags!(target_tag, [source_tag])
+
+      expect(version.reload).to have_attributes(
+          tag_id: source_tag.id, tag_name: source_tag_name.name, tag_category: 'material')
+      expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+      expect(material.reload.tag).to eq(target_tag)
+    end
+
     context 'when source_tags includes the target itself' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
       it 'ignores the target in source_tags while still merging the source tag' do
         described_class.merge_tags!(target_tag, [source_tag, target_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
-        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
+        target_link = PostTag.find_by(post: post_record, tag: target_tag)
 
         expect(Tag.find(target_tag.id)).to be_present
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
-        expect(source_pt.discarded_at).to be_present
-        expect(source_pt.tag_id).to eq(source_tag.id)
-        expect(active_target).to be_present
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
+        expect(target_link).to be_present
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -260,18 +622,17 @@ RSpec.describe Tag, type: :model do
         )
       end
 
-      it 'still merges, but discards the source tag_name instead of aliasing it' do
+      it 'still merges and keeps the source name as an alias without validating it' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
-        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
-        discarded_source_tag_name = TagName.with_discarded.find(source_tag_name.id)
+        target_link = PostTag.find_by(post: post_record, tag: target_tag)
 
-        expect(source_pt.discarded_at).to be_present
-        expect(source_pt.tag_id).to eq(source_tag.id)
-        expect(active_target).to be_present
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
+        expect(target_link).to be_present
 
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -288,34 +649,30 @@ RSpec.describe Tag, type: :model do
             message: 'init')
       end
 
-      it 'rolls back the transaction' do
+      it 'rolls back earlier deletions, links, and history when a later source has a wiki' do
+        earlier_source = create(:tag)
+        earlier_name = primary_tag_name_for(earlier_source, 'ja')
+        source_section = create(:post_tag_section, post: post_record,
+                                                   tag: source_tag,
+                                                   begin_ms: 1000, end_ms: 2000)
+
         expect {
-          described_class.merge_tags!(target_tag, [source_tag])
+          described_class.merge_tags!(target_tag, [earlier_source, source_tag])
         }.to raise_error(ActiveRecord::RecordInvalid)
 
-        expect(Tag.with_discarded.find(source_tag.id)).not_to be_discarded
-        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
-        expect(PostTag.kept.find(source_post_tag.id).tag_id).to eq(source_tag.id)
-        expect(PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)).to be_nil
-        expect(source_tag_name.reload.canonical_id).to be_nil
-        expect(target_tag.reload.post_count).to eq(0)
-      end
-    end
-
-    context 'when merging a nico source tag' do
-      let!(:target_tag) { create(:tag, category: :nico, name: 'nico:foo') }
-      let!(:source_tag) { create(:tag, category: :nico, name: 'nico:bar') }
-      let!(:source_tag_name_id) { source_tag.tag_name_id }
-
-      it 'discards the source tag_name instead of aliasing it' do
-        described_class.merge_tags!(target_tag, [source_tag])
-
-        discarded_source_tag = Tag.with_discarded.find(source_tag.id)
-        discarded_source_tag_name = TagName.with_discarded.find(source_tag_name_id)
-
-        expect(discarded_source_tag).to be_discarded
-        expect(discarded_source_tag_name).to be_discarded
-        expect(discarded_source_tag_name.canonical_id).to be_nil
+        expect(Tag.unscoped.exists?(earlier_source.id)).to be(true)
+        expect(earlier_name.reload).to have_attributes(
+            tag_id: earlier_source.id, language_code: 'ja', primary_flg: true)
+        expect(TagVersion.where(tag_id: [earlier_source.id, source_tag.id, target_tag.id]))
+            .to be_empty
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(true)
+        expect(TagName.unscoped.exists?(source_tag_name.id)).to be(true)
+        expect(source_post_tag.reload.tag_id).to eq(source_tag.id)
+        expect(source_post_tag.sections).to contain_exactly(source_section)
+        expect(PostTag.find_by(post: post_record, tag: target_tag)).to be_nil
+        expect(source_tag.reload.post_count).to eq(1)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: source_tag.id, language_code: 'ja', primary_flg: true)
         expect(target_tag.reload.post_count).to eq(0)
       end
     end
@@ -333,6 +690,7 @@ RSpec.describe Tag, type: :model do
         url: post.url,
         thumbnail_base: post.thumbnail_base,
         tags: snapshot_tags(post),
+        tags_json: post.snapshot_tags_json,
         parent_post_ids: post.snapshot_parent_post_ids.join(' '),
         original_created_from: post.original_created_from,
         original_created_before: post.original_created_before,
@@ -364,12 +722,15 @@ RSpec.describe Tag, type: :model do
         expect(latest.event_type).to eq('update')
         expect(latest.created_by_user).to be_nil
         expect(latest.tags).to eq(snapshot_tags(post_record.reload))
+        expect(latest.tags_json.map { |item| item.fetch('tag_id') }).to eq([target_tag.id])
+        expect(affected_versions.first.tags_json.map { |item| item.fetch('tag_id') })
+            .to eq([source_tag.id])
 
         expect(unaffected_post.reload.post_versions.count).to eq(1)
       end
     end
 
-    context 'when the source tag has no active post_tags' do
+    context 'when the source tag has no post_tags' do
       let!(:another_post) do
         Post.create!(url: 'https://example.com/posts/3', title: 'another post')
       end

backend/spec/models/version_record_spec.rb

@@ -1,21 +1,22 @@
 require 'rails_helper'
 
 RSpec.describe VersionRecord, type: :model do
-  let!(:tag) { create(:tag, name: 'version_record_tag') }
-  let!(:nico_tag) { create(:tag, :nico, name: 'nico:version_record_tag') }
+  let!(:tag) { create(:tag, primary_name: 'version_record_tag') }
+  let!(:nico_tag) { create(:external_tag, name: 'version_record_tag') }
 
   it 'makes TagVersion read only after create' do
     version = TagVersion.create!(
       tag: tag,
       version_no: 1,
       event_type: 'create',
-      name: tag.name,
+      name: primary_tag_name_for(tag, 'ja').name,
       category: tag.category,
       aliases: '',
+      names: { ja: { name: primary_tag_name_for(tag, 'ja').name,
+                     script_code: 'Jpan', auto_generated: false, aliases: [] } },
       parent_tag_ids: '',
       created_at: Time.current,
-      created_by_user: nil
-    )
+      created_by_user: nil)
 
     expect {
       version.update!(name: 'changed')
@@ -27,13 +28,14 @@ RSpec.describe VersionRecord, type: :model do
       tag: tag,
       version_no: 1,
       event_type: 'create',
-      name: tag.name,
+      name: primary_tag_name_for(tag, 'ja').name,
       category: tag.category,
       aliases: '',
+      names: { ja: { name: primary_tag_name_for(tag, 'ja').name,
+                     script_code: 'Jpan', auto_generated: false, aliases: [] } },
       parent_tag_ids: '',
       created_at: Time.current,
-      created_by_user: nil
-    )
+      created_by_user: nil)
 
     expect {
       version.destroy!
@@ -42,10 +44,10 @@ RSpec.describe VersionRecord, type: :model do
 
   it 'makes NicoTagVersion read only after create' do
     version = NicoTagVersion.create!(
-      tag: nico_tag,
+      external_tag: nico_tag,
       version_no: 1,
       event_type: 'create',
-      name: nico_tag.name,
+      name: "nico:#{ nico_tag.name }",
       linked_tags: '',
       created_at: Time.current,
       created_by_user: nil
@@ -58,10 +60,10 @@ RSpec.describe VersionRecord, type: :model do
 
   it 'prevents NicoTagVersion destroy' do
     version = NicoTagVersion.create!(
-      tag: nico_tag,
+      external_tag: nico_tag,
       version_no: 1,
       event_type: 'create',
-      name: nico_tag.name,
+      name: "nico:#{ nico_tag.name }",
       linked_tags: '',
       created_at: Time.current,
       created_by_user: nil

backend/spec/requests/deerjikists_spec.rb

@@ -30,7 +30,7 @@ RSpec.describe 'Deerjikists API', type: :request do
 
         expect(json['tag']).to be_a(Hash)
         expect(json['tag']['id']).to eq(tag1.id)
-        expect(json['tag']['name']).to eq(tag1.name)
+        expect(json['tag']['name']).to eq(primary_tag_name_for(tag1, 'ja').name)
       end
     end
 

backend/spec/requests/error_responses_spec.rb

@@ -15,7 +15,7 @@ RSpec.describe 'error responses', type: :request do
 
     it 'returns a stable field-error payload for unprocessable requests' do
       member = create(:user, :member)
-      tag = create(:tag, :general, name: 'error_response_tag')
+      tag = create(:tag, category: :general, primary_name: 'error_response_tag')
       sign_in_as(member)
 
       patch "/tags/#{ tag.id }", params: { category: 'nico' }

backend/spec/requests/gekanator_learning_spec.rb

@@ -898,23 +898,22 @@ RSpec.describe 'Gekanator learning API', type: :request do
 
   describe 'GET /gekanator/questions' do
     it 'omits questions for deprecated tags' do
-      active_tag = Tag.create!(name: 'active_question_tag', category: :general)
-      deprecated_tag = Tag.create!(
-        name: 'deprecated_question_tag',
-        category: :general,
-        deprecated_at: Time.current
-      )
+      active_tag = create(:tag, primary_name: 'active_question_tag', category: :general)
+      deprecated_tag = create(:tag,
+          primary_name: 'deprecated_question_tag',
+          category: :general,
+          deprecated_at: Time.current)
 
       [active_tag, deprecated_tag].each do |question_tag|
         GekanatorQuestion.create!(
-          text: "#{ question_tag.name }?",
+          text: "#{ primary_tag_name_for(question_tag, 'ja').name }?",
           kind: 'tag',
           source: 'admin_curated',
           status: 'accepted',
           priority_weight: 1.0,
           condition: {
             type: 'tag',
-            key: "#{ question_tag.category }:#{ question_tag.name }"
+            key: "#{ question_tag.category }:#{ primary_tag_name_for(question_tag, 'ja').name }"
           },
           created_by: admin
         )

backend/spec/requests/gekanator_posts_spec.rb

@@ -4,12 +4,11 @@ require 'rails_helper'
 RSpec.describe 'Gekanator posts API', type: :request do
   describe 'GET /gekanator/posts' do
     it 'omits deprecated tags and returns the stored similarity cosine' do
-      active_tag = Tag.create!(name: 'active tag', category: :general)
-      deprecated_tag = Tag.create!(
-        name: 'deprecated tag',
-        category: :general,
-        deprecated_at: Time.current
-      )
+      active_tag = create(:tag, primary_name: 'active tag', category: :general)
+      deprecated_tag = create(:tag,
+          primary_name: 'deprecated tag',
+          category: :general,
+          deprecated_at: Time.current)
       post_record = Post.create!(title: 'source', url: 'https://example.com/source')
       target_post = Post.create!(title: 'target', url: 'https://example.com/target')
 

backend/spec/requests/locale_write_paths_spec.rb

@@ -0,0 +1,363 @@
+require 'rails_helper'
+
+RSpec.describe 'Locale propagation on write paths', type: :request do
+  include_context 'English locale'
+
+  let(:member) { create(:user, :member) }
+
+  before do
+    sign_in_as(member)
+  end
+
+  def expect_localised_tag(name, expected_locale)
+    tag_name = TagName.find_by!(name:, language_code: expected_locale.language_code)
+    expect(tag_name).to have_attributes(
+        script_code: expected_locale.script_code, primary_flg: true)
+    expect(tag_name.tag_id).to be_present
+    tag_name.tag
+  end
+
+  it 'confirms a generated Nipponese primary when a human renames it' do
+    tag = create(:tag, primary_name: 'generated_source')
+    primary = primary_tag_name_for(tag, 'ja')
+    primary.update!(name: "Tag_##{ tag.id }", auto_generated: true)
+
+    patch "/tags/#{ tag.id }", params: { locale: 'ja', name: '人間が確定した名称' }
+
+    expect(response).to have_http_status(:ok), response.body
+    expect(primary.reload).to have_attributes(
+        name: '人間が確定した名称', auto_generated: false)
+  end
+
+  it 'rolls back Nipponese edits when an alias conflicts with another primary' do
+    tag = create(:tag, primary_name: 'target_before_collision')
+    create(:tag_name, :alias, tag:, name: 'existing_alias')
+    other_tag = create(:tag, primary_name: 'other_primary')
+    other_primary = primary_tag_name_for(other_tag, 'ja')
+    primary_name_before = primary_tag_name_for(tag, 'ja').name
+    aliases_before = tag.tag_names.where(primary_flg: false).order(:name).pluck(:name)
+    category_before = tag.category
+
+    put "/tags/#{ tag.id }", params: {
+        locale: 'ja', name: 'renamed_before_collision', category: 'character',
+        deprecated: false, aliases: 'other_primary', parent_tags: '' }
+
+    aggregate_failures do
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(other_primary.reload).to have_attributes(tag_id: other_tag.id, primary_flg: true)
+      expect(TagName.where(tag: other_tag, language_code: 'ja', primary_flg: true))
+          .to contain_exactly(other_primary)
+      expect(primary_tag_name_for(tag.reload, 'ja').name).to eq(primary_name_before)
+      expect(tag.category).to eq(category_before)
+      expect(tag.tag_names.where(primary_flg: false).order(:name).pluck(:name))
+          .to eq(aliases_before)
+    end
+  end
+
+  ['en', nil].each do |requested_locale|
+    context "with locale #{ requested_locale.inspect }" do
+      let(:locale_params) { requested_locale ? { locale: requested_locale } : { } }
+      let(:expected_locale) { requested_locale ? locale : Locale.nipponese }
+
+      it 'creates post tags in the requested language or Nipponese fallback' do
+        pending '日本語以外の Locale 有効化は別課題で実装する' if requested_locale
+        locale if requested_locale
+        post '/posts', params: locale_params.merge(
+            title: 'Locale post', url: 'https://example.com/locale-post',
+            tags: 'locale_post_tag', parent_post_ids: '')
+
+        expect(response).to have_http_status(:created), response.body
+        tag = expect_localised_tag('locale_post_tag', expected_locale)
+        expect(Post.find(json.fetch('id')).tags).to include(tag)
+      end
+
+      it 'updates post tags in the requested language or Nipponese fallback' do
+        pending '日本語以外の Locale 有効化は別課題で実装する' if requested_locale
+        locale if requested_locale
+        record = create(:post)
+        PostVersionRecorder.record!(post: record, event_type: :create, created_by_user: member)
+
+        put "/posts/#{ record.id }", params: locale_params.merge(
+            title: record.title, tags: 'locale_updated_tag', parent_post_ids: '',
+            base_version_no: record.reload.version_no)
+
+        expect(response).to have_http_status(:ok), response.body
+        tag = expect_localised_tag('locale_updated_tag', expected_locale)
+        expect(record.reload.tags).to include(tag)
+      end
+
+      it 'passes the resolved locale to bulk creation' do
+        pending '日本語以外の Locale 有効化は別課題で実装する' if requested_locale
+        locale if requested_locale
+        # Worker propagation is exercised in post_bulk_creator_spec.
+        expect_any_instance_of(PostBulkCreator).to receive(:run)
+            .with(expected_locale).and_return(results: [])
+        manifest = [{ title: 'Bulk locale', url: 'https://example.com/bulk-locale',
+                      tags: 'bulk_locale_tag', parent_post_ids: '' }]
+
+        post '/posts/bulk', params: locale_params.merge(posts: JSON.generate(manifest)),
+                            headers: { 'CONTENT_TYPE' => 'multipart/form-data' }
+
+        expect(response).to have_http_status(:ok), response.body
+      end
+
+      it 'creates materials with tags in the resolved locale' do
+        pending '日本語以外の Locale 有効化は別課題で実装する' if requested_locale
+        locale if requested_locale
+        post '/materials', params: locale_params.merge(
+            tag: 'locale_material', url: 'https://example.com/material')
+
+        expect(response).to have_http_status(:created), response.body
+        tag = expect_localised_tag('locale_material', expected_locale)
+        expect(Material.find(json.fetch('id')).tag).to eq(tag)
+      end
+
+      it 'updates materials with tags in the resolved locale' do
+        pending '日本語以外の Locale 有効化は別課題で実装する' if requested_locale
+        locale if requested_locale
+        tag = create(:tag, category: :material)
+        material = Material.create!(tag:, url: 'https://example.com/material')
+
+        put "/materials/#{ material.id }", params: locale_params.merge(
+            tag: 'locale_material_updated', url: material.url)
+
+        expect(response).to have_http_status(:ok), response.body
+        resolved_tag = expect_localised_tag('locale_material_updated', expected_locale)
+        expect(material.reload.tag).to eq(resolved_tag)
+      end
+
+      it 'links Nico external tags to internal tags in the resolved locale' do
+        pending '日本語以外の Locale 有効化は別課題で実装する' if requested_locale
+        locale if requested_locale
+        external = create(:external_tag)
+        NicoTagVersionRecorder.record!(
+            external_tag: external, event_type: :create, created_by_user: member)
+
+        put "/tags/nico/#{ external.id }", params: locale_params.merge(tags: 'locale_link')
+
+        expect(response).to have_http_status(:ok), response.body
+        tag = expect_localised_tag('locale_link', expected_locale)
+        expect(external.reload.linked_tags).to contain_exactly(tag)
+      end
+
+      it 'creates parent tags in the resolved locale' do
+        pending '日本語以外の Locale 有効化は別課題で実装する' if requested_locale
+        locale if requested_locale
+        tag = create(:tag)
+
+        put "/tags/#{ tag.id }", params: locale_params.merge(
+            name: primary_tag_name_for(tag, 'ja').name, category: tag.category, deprecated: false,
+            aliases: '', parent_tags: 'locale_parent')
+
+        expect(response).to have_http_status(:ok), response.body
+        parent = expect_localised_tag('locale_parent', expected_locale)
+        expect(TagImplication.where(tag:).pluck(:parent_tag_id)).to eq([parent.id])
+      end
+    end
+  end
+
+  context 'with existing names in both languages' do
+    let(:english_name) do
+      create(:tag_name, name: 'shared_name', language_code: 'en', script_code: 'Latn')
+    end
+    let(:english_tag) { create(:tag, primary_tag_name: english_name, category: :material) }
+    let(:nipponese_tag) do
+      create(:tag, primary_name: 'temporary_nipponese', category: :general).tap do |tag|
+        # Isolate lookup from the separately tested uniqueness validation.
+        primary_tag_name_for(tag, 'ja').update_columns(name: 'shared_name')
+      end
+    end
+
+    it 'plans and creates the post using the English identity and category' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      english_tag
+      nipponese_tag
+      post '/posts', params: {
+          locale: 'en', title: 'English identity',
+          url: 'https://example.com/english-identity', tags: 'shared_name', parent_post_ids: '' }
+
+      expect(response).to have_http_status(:created), response.body
+      record = Post.find(json.fetch('id'))
+      expect(record.tags).to include(english_tag)
+      expect(record.tags).not_to include(nipponese_tag)
+      expect(english_tag.reload.category).to eq('material')
+      expect(nipponese_tag.reload.category).to eq('general')
+    end
+
+    it 'updates the post using the English identity' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      english_tag
+      nipponese_tag
+      record = create(:post)
+      PostVersionRecorder.record!(post: record, event_type: :create, created_by_user: member)
+
+      put "/posts/#{ record.id }", params: {
+          locale: 'en', title: record.title, tags: 'shared_name', parent_post_ids: '',
+          base_version_no: record.reload.version_no }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(record.reload.tags).to include(english_tag)
+      expect(record.tags).not_to include(nipponese_tag)
+    end
+
+    it 'resolves the English material tag' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      english_tag
+      nipponese_tag
+      post '/materials', params: {
+          locale: 'en', tag: 'shared_name', url: 'https://example.com/english-material' }
+
+      expect(response).to have_http_status(:created), response.body
+      expect(Material.find(json.fetch('id')).tag).to eq(english_tag)
+      expect(Material.where(tag: nipponese_tag)).to be_empty
+    end
+
+    it 'resolves the English parent tag' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      english_tag
+      nipponese_tag
+      child = create(:tag)
+
+      put "/tags/#{ child.id }", params: {
+          locale: 'en', name: primary_tag_name_for(child, 'ja').name,
+          category: child.category, deprecated: false,
+          aliases: '', parent_tags: 'shared_name' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(TagImplication.where(tag: child).pluck(:parent_tag_id)).to eq([english_tag.id])
+    end
+
+    it 'resolves the English internal tag for a Nico link' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      english_tag
+      nipponese_tag
+      external = create(:external_tag)
+      NicoTagVersionRecorder.record!(
+          external_tag: external, event_type: :create, created_by_user: member)
+
+      put "/tags/nico/#{ external.id }", params: { locale: 'en', tags: 'shared_name' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(external.reload.linked_tags).to contain_exactly(english_tag)
+    end
+  end
+
+  context 'when renaming or updating aliases in English' do
+    let(:english_name) do
+      create(:tag_name, name: 'english_original', language_code: 'en', script_code: 'Latn')
+    end
+    let(:tag) { create(:tag, primary_tag_name: english_name) }
+
+    it 'marks a human-renamed generated primary as no longer auto-generated' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      generated_tag = create(:tag, primary_name: 'rename_generated_source')
+      generated_name = primary_tag_name_for(generated_tag, 'en')
+      expect(generated_name.auto_generated).to be(true)
+
+      patch "/tags/#{ generated_tag.id }", params: {
+          locale: 'en', name: 'human_english_name' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(generated_name.reload).to have_attributes(
+          name: 'human_english_name', auto_generated: false)
+    end
+
+    it 'does not steal another tag primary for an alias' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      other_tag = create(:tag, primary_name: 'other_nipponese')
+      other_primary = primary_tag_name_for(other_tag, 'en')
+      other_primary.update!(name: 'other_english_primary', auto_generated: false)
+      create(:tag_name, :alias, tag:, name: 'existing_english_alias',
+                                language_code: 'en', script_code: 'Latn')
+      primary_name_before = primary_tag_name_for(tag, 'en').name
+      aliases_before =
+          tag.tag_names.where(language_code: 'en', primary_flg: false)
+              .order(:name).pluck(:name)
+      category_before = tag.category
+
+      put "/tags/#{ tag.id }", params: {
+          locale: 'en', name: 'renamed_before_alias_collision',
+          category: 'character', deprecated: false,
+          aliases: 'other_english_primary', parent_tags: '' }
+
+      aggregate_failures do
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(other_primary.reload).to have_attributes(
+            tag_id: other_tag.id, language_code: 'en', primary_flg: true)
+        expect(TagName.where(tag: other_tag, language_code: 'en', primary_flg: true))
+            .to contain_exactly(other_primary)
+        expect(primary_tag_name_for(tag.reload, 'en').name).to eq(primary_name_before)
+        expect(tag.category).to eq(category_before)
+        aliases_after =
+            tag.tag_names.where(language_code: 'en', primary_flg: false)
+                .order(:name).pluck(:name)
+        expect(aliases_after).to eq(aliases_before)
+      end
+    end
+
+    it 'allows a rename to a name already used in Nipponese' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      nipponese = create(:tag, primary_name: 'rename_target')
+
+      patch "/tags/#{ tag.id }", params: { locale: 'en', name: 'rename_target' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(primary_tag_name_for(tag.reload, 'en')).to have_attributes(
+          name: 'rename_target', language_code: 'en', tag_id: tag.id)
+      expect(primary_tag_name_for(nipponese.reload, 'ja')).to have_attributes(
+          name: 'rename_target', language_code: 'ja', tag_id: nipponese.id)
+    end
+
+    it 'creates aliases in the requested language' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      put "/tags/#{ tag.id }", params: {
+          locale: 'en', name: english_name.name,
+          category: tag.category, deprecated: false,
+          aliases: 'english_alias', parent_tags: '' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(TagName.find_by!(language_code: 'en', name: 'english_alias'))
+          .to have_attributes(
+              script_code: 'Latn',
+              tag_id: tag.id, primary_flg: false, language_code: 'en')
+      primary = TagName.find_by!(tag_id: tag.id, language_code: 'en', primary_flg: true)
+      expect(primary).to have_attributes(name: 'english_original', script_code: 'Latn')
+    end
+
+    it 'does not take an alias from another language' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      nipponese = create(:tag, primary_name: 'nipponese_owner')
+      nipponese_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                  tag: nipponese)
+      expect(nipponese_alias.reload).to have_attributes(
+          tag_id: nipponese.id,
+          primary_flg: false, language_code: 'ja')
+
+      put "/tags/#{ tag.id }", params: {
+          locale: 'en', name: english_name.name,
+          category: tag.category, deprecated: false,
+          aliases: 'shared_alias', parent_tags: '' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(nipponese_alias.reload).to have_attributes(
+          tag_id: nipponese.id,
+          primary_flg: false, language_code: 'ja')
+      expect(TagName.find_by!(language_code: 'en', name: 'shared_alias'))
+          .to have_attributes(
+              tag_id: tag.id, script_code: 'Latn',
+              primary_flg: false, language_code: 'en')
+      expect(TagName.where(name: 'shared_alias').pluck(:language_code, :tag_id))
+          .to contain_exactly(['ja', nipponese.id], ['en', tag.id])
+    end
+  end
+end

backend/spec/requests/materials_spec.rb

@@ -26,10 +26,10 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'GET /materials' do
     let!(:tag_a) do
-      Tag.create!(tag_name: TagName.create!(name: 'material_index_a'), category: :material)
+      create(:tag, primary_name: 'material_index_a', category: :material)
     end
     let!(:tag_b) do
-      Tag.create!(tag_name: TagName.create!(name: 'material_index_b'), category: :material)
+      create(:tag, primary_name: 'material_index_b', category: :material)
     end
 
     let!(:material_a) do
@@ -116,20 +116,20 @@ RSpec.describe 'Materials API', type: :request do
 
     it 'filters by descendant tags and returns stable parent tag groups' do
       root =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_root'),
+          create(:tag, primary_name: 'material_scope_root',
                       category: :material)
       child_b =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_b'),
+          create(:tag, primary_name: 'material_scope_b',
                       category: :material)
       child_a =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_a'),
+          create(:tag, primary_name: 'material_scope_a',
                       category: :material)
       deprecated =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_old'),
+          create(:tag, primary_name: 'material_scope_old',
                       category: :material,
                       deprecated_at: Time.current)
       grandchild =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_grandchild'),
+          create(:tag, primary_name: 'material_scope_grandchild',
                       category: :material)
       root_material =
           build_material(tag: root, user: member_user,
@@ -179,7 +179,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'GET /materials/:id' do
     let!(:tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'material_show'), category: :material)
+      create(:tag, primary_name: 'material_show', category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'show.png'))
@@ -269,7 +269,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:created)
 
         material = Material.order(:id).last
-        expect(material.tag.name).to eq('material_create_new')
+        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_create_new')
         expect(material.tag.category).to eq('material')
         expect(material.created_by_user).to eq(member_user)
         expect(material.updated_by_user).to eq(member_user)
@@ -297,7 +297,8 @@ RSpec.describe 'Materials API', type: :request do
 
         expect(response).to have_http_status(:created)
 
-        tag = Tag.joins(:tag_name).find_by!(tag_names: { name: 'material_create_versioned_tag' })
+        tag = TagName.find_by!(name: 'material_create_versioned_tag',
+                               language_code: 'ja', primary_flg: true).tag
         version = tag.tag_versions.order(:version_no).last
 
         expect(version.event_type).to eq('create')
@@ -323,8 +324,8 @@ RSpec.describe 'Materials API', type: :request do
       end
 
       it 'returns 422 when the existing tag is not material/character' do
-        general_tag_name = TagName.create!(name: 'material_create_general_tag')
-        Tag.create!(tag_name: general_tag_name, category: :general)
+        general_tag_name = create(:tag_name, name: 'material_create_general_tag')
+        create(:tag, primary_tag_name: general_tag_name, category: :general)
 
         post '/materials', params: {
           tag: 'material_create_general_tag',
@@ -345,7 +346,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:created)
 
         material = Material.order(:id).last
-        expect(material.tag.name).to eq('material_create_url_only')
+        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_create_url_only')
         expect(material.url).to eq('https://example.com/material-source')
         expect(material.file.attached?).to be(false)
       end
@@ -384,7 +385,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'PUT /materials/:id' do
     let!(:tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'material_update_old'), category: :material)
+      create(:tag, primary_name: 'material_update_old', category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'old.png'))
@@ -463,7 +464,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:ok)
 
         material.reload
-        expect(material.tag.name).to eq('material_update_new')
+        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_update_new')
         expect(material.tag.category).to eq('material')
         expect(material.url).to eq('https://example.com/updated-source')
         expect(material.updated_by_user).to eq(member_user)
@@ -497,7 +498,8 @@ RSpec.describe 'Materials API', type: :request do
 
         expect(response).to have_http_status(:ok)
 
-        tag = Tag.joins(:tag_name).find_by!(tag_names: { name: 'material_update_versioned_tag' })
+        tag = TagName.find_by!(name: 'material_update_versioned_tag',
+                               language_code: 'ja', primary_flg: true).tag
         version = tag.tag_versions.order(:version_no).last
 
         expect(version.event_type).to eq('create')
@@ -508,7 +510,7 @@ RSpec.describe 'Materials API', type: :request do
 
       it 'backfills a create tag_version for an existing material tag without history' do
         existing_tag =
-            Tag.create!(tag_name: TagName.create!(name: 'material_update_existing_no_history'),
+            create(:tag, primary_name: 'material_update_existing_no_history',
                         category: :material)
 
         expect(existing_tag.tag_versions).to be_empty
@@ -531,7 +533,7 @@ RSpec.describe 'Materials API', type: :request do
 
       it 'backfills a create tag_version for an existing character tag without history' do
         existing_tag =
-            Tag.create!(tag_name: TagName.create!(name: 'material_update_character_no_history'),
+            create(:tag, primary_name: 'material_update_character_no_history',
                         category: :character)
 
         expect(existing_tag.tag_versions).to be_empty
@@ -563,7 +565,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:ok)
 
         material.reload
-        expect(material.tag.name).to eq('material_update_remove_file')
+        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_update_remove_file')
         expect(material.url).to eq('https://example.com/updated-source')
         expect(material.updated_by_user).to eq(member_user)
         expect(material.file.attached?).to be(false)
@@ -651,8 +653,8 @@ RSpec.describe 'Materials API', type: :request do
   end
 
   describe 'GET /materials/download.zip' do
-    let!(:tag_a) { Tag.create!(tag_name: TagName.create!(name: 'zip_a'), category: :material) }
-    let!(:tag_b) { Tag.create!(tag_name: TagName.create!(name: 'zip_b'), category: :material) }
+    let!(:tag_a) { create(:tag, primary_name: 'zip_a', category: :material) }
+    let!(:tag_b) { create(:tag, primary_name: 'zip_b', category: :material) }
     let!(:material_a) do
       build_material(tag: tag_a, user: member_user,
                      file: dummy_upload(filename: 'a.png', body: 'zip-a'))
@@ -701,7 +703,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'GET /materials/versions' do
     let!(:tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'material_history'), category: :material)
+      create(:tag, primary_name: 'material_history', category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'history.png'))
@@ -776,7 +778,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'DELETE /materials/:id' do
     let!(:tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'material_destroy'), category: :material)
+      create(:tag, primary_name: 'material_destroy', category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'destroy.png'))

backend/spec/requests/nico_tags_spec.rb

@@ -3,10 +3,34 @@ require 'rails_helper'
 
 RSpec.describe 'NicoTags', type: :request do
   describe 'GET /tags/nico' do
-    it 'returns paginated tags and total count' do
-      create_list(:tag, 3, :nico)
+    it 'returns the legacy Tag-compatible external fields' do
+      external = create(:external_tag, name: 'legacy_external', post_count: 3)
 
-      get '/tags/nico', params: { page: 2, limit: 2 }
+      get '/tags/nico', params: { name: 'legacy_external' }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('count')).to eq(1)
+      expect(json.fetch('tags')).to contain_exactly(
+          a_hash_including(
+              'id' => external.id,
+              'name' => 'nico:legacy_external',
+              'category' => 'nico',
+              'post_count' => 3,
+              'created_at' => external.created_at.as_json,
+              'updated_at' => external.created_at.as_json,
+              'deprecated_at' => nil,
+              'aliases' => [],
+              'parents' => [],
+              'has_wiki' => false,
+              'material_id' => nil,
+              'has_deerjikists' => false,
+              'linked_tags' => []))
+    end
+
+    it 'returns paginated tags and total count' do
+      3.times { |i| create(:external_tag, name: "pagination_#{ i }") }
+
+      get '/tags/nico', params: { page: 2, limit: 2, name: 'pagination_' }
 
       expect(response).to have_http_status(:ok)
       expect(json['tags'].size).to eq(1)
@@ -14,16 +38,16 @@ RSpec.describe 'NicoTags', type: :request do
     end
 
     it 'filters by nico tag name, linked tag name, and link status' do
-      linked = create(:tag, :nico)
-      linked.tag_name.update!(name: 'nico:search_linked')
-      unlinked = create(:tag, :nico)
-      unlinked.tag_name.update!(name: 'nico:search_unlinked')
-      other = create(:tag, :nico)
-      other.tag_name.update!(name: 'nico:other')
-      destination = create(:tag, :general)
-      destination.tag_name.update!(name: 'destination_search')
+      linked = create(:external_tag)
+      linked.update!(name: 'search_linked')
+      unlinked = create(:external_tag)
+      unlinked.update!(name: 'search_unlinked')
+      other = create(:external_tag)
+      other.update!(name: 'other')
+      destination = create(:tag, category: :general)
+      primary_tag_name_for(destination, 'ja').update!(name: 'destination_search')
       NicoTagRelation.create!(nico_tag: linked, tag: destination)
-      NicoTagRelation.create!(nico_tag: other, tag: create(:tag, :general))
+      NicoTagRelation.create!(nico_tag: other, tag: create(:tag, category: :general))
 
       get '/tags/nico', params: {
         name: 'search_',
@@ -41,37 +65,77 @@ RSpec.describe 'NicoTags', type: :request do
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([unlinked.id])
     end
 
+    it 'filters by the qualified legacy name as well as the raw name' do
+      external = create(:external_tag, name: 'qualified_filter')
+      create(:external_tag, name: 'unrelated_filter')
+
+      ['qualified_filter', 'nico:qualified_filter'].each do |name|
+        get '/tags/nico', params: { name: }
+
+        expect(response).to have_http_status(:ok)
+        expect(json.fetch('count')).to eq(1)
+        expect(json.fetch('tags')).to contain_exactly(
+            a_hash_including('id' => external.id, 'name' => 'nico:qualified_filter'))
+      end
+    end
+
     it 'sorts by name and timestamps' do
-      older = create(:tag, :nico)
-      older.tag_name.update!(name: 'nico:a')
+      older = create(:external_tag)
+      older.update!(name: 'ordered_a')
       older.update_columns(created_at: 2.days.ago)
-      newer = create(:tag, :nico)
-      newer.tag_name.update!(name: 'nico:b')
+      newer = create(:external_tag)
+      newer.update!(name: 'ordered_b')
       newer.update_columns(created_at: 1.day.ago)
       older_post_tag =
-        PostTag.create!(post: Post.create!(url: 'https://example.com/nico-older'), tag: older)
+        PostExternalTag.create!(post: create(:post), external_tag: older)
       older_post_tag.update_columns(created_at: 1.hour.ago)
       newer_post_tag =
-        PostTag.create!(post: Post.create!(url: 'https://example.com/nico-newer'), tag: newer)
+        PostExternalTag.create!(post: create(:post), external_tag: newer)
       newer_post_tag.update_columns(created_at: 2.hours.ago)
 
-      get '/tags/nico', params: { order: 'name:desc' }
+      get '/tags/nico', params: { order: 'name:desc', name: 'ordered_' }
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([newer.id, older.id])
 
-      get '/tags/nico', params: { order: 'created_at:asc' }
+      get '/tags/nico', params: { order: 'created_at:asc', name: 'ordered_' }
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([older.id, newer.id])
 
-      get '/tags/nico', params: { order: 'updated_at:desc' }
+      get '/tags/nico', params: { order: 'updated_at:desc', name: 'ordered_' }
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([older.id, newer.id])
       expect(Time.zone.parse(json.fetch('tags').first.fetch('recent_post_tag_created_at')))
         .to be_within(1.second).of(older_post_tag.created_at)
     end
   end
 
+  describe 'GET /tags/nico/:id' do
+    it 'returns the external tag even when an internal tag has the same id' do
+      internal = create(:tag)
+      external = create(
+          :external_tag,
+          id: internal.id,
+          name: 'external_detail')
+
+      get "/tags/nico/#{ external.id }"
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'id' => external.id,
+          'name' => 'nico:external_detail',
+          'category' => 'nico')
+    end
+
+    it 'returns 404 when the external tag does not exist' do
+      internal = create(:tag)
+
+      get "/tags/nico/#{ internal.id }"
+
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
   describe 'PATCH /tags/nico/:id' do
     let(:member) { create(:user, :member) }
     let(:admin) { create(:user, :admin) }
-    let(:nico_tag) { create(:tag, :nico) }
+    let(:nico_tag) { create(:external_tag) }
 
     it '401 when not logged in' do
       sign_out
@@ -85,30 +149,31 @@ RSpec.describe 'NicoTags', type: :request do
       expect(response).to have_http_status(:forbidden)
     end
 
-    it '400 when target is not nico category' do
+    it '404 when only an internal tag exists for the target id' do
       sign_in_as(member)
-      non_nico = create(:tag, :general)
+      non_nico = create(:tag, category: :general)
+      expect(ExternalTag.exists?(non_nico.id)).to be(false)
       patch "/tags/nico/#{non_nico.id}", params: { tags: 'a b' }
-      expect(response).to have_http_status(:bad_request)
+      expect(response).to have_http_status(:not_found)
     end
 
     it '200 and updates linked tags while recording tag versions' do
       sign_in_as(admin)
 
-      nico_tag_name = TagName.create!(name: 'nico:nico_tags_spec_source')
-      nico_tag = Tag.create!(tag_name: nico_tag_name, category: :nico)
+      nico_tag = create(:external_tag, name: 'nico_tags_spec_source')
 
-      linked_a_name = TagName.create!(name: 'nico_linked_a')
-      linked_a = Tag.create!(tag_name: linked_a_name, category: :general)
+      linked_a_name = create(:tag_name, name: 'nico_linked_a')
+      linked_a = create(:tag, primary_tag_name: linked_a_name, category: :general)
 
-      linked_b_name = TagName.create!(name: 'nico_linked_b')
-      linked_b = Tag.create!(tag_name: linked_b_name, category: :general)
+      linked_b_name = create(:tag_name, name: 'nico_linked_b')
+      linked_b = create(:tag, primary_tag_name: linked_b_name, category: :general)
 
-      TagVersioning.ensure_snapshot!(nico_tag, created_by_user: admin)
+      NicoTagVersionRecorder.record!(external_tag: nico_tag,
+                                     event_type: :create, created_by_user: admin)
 
       expect {
         patch "/tags/nico/#{nico_tag.id}", params: {
-          tags: "  #{linked_a.name}\n#{linked_b.name}  "
+          tags: "  #{ linked_a_name.name }\n#{ linked_b_name.name }  "
         }
       }.to change(TagVersion, :count).by(2)
        .and change(NicoTagVersion, :count).by(1)
@@ -126,26 +191,26 @@ RSpec.describe 'NicoTags', type: :request do
       expect(versions.map(&:event_type)).to eq(['create', 'update'])
       expect(versions.last.linked_tags.split).to match_array([
         'nico_linked_a',
-        'nico_linked_b'
-      ])
+        'nico_linked_b'])
       expect(versions.last.created_by_user_id).to eq(admin.id)
     end
 
-    it 'returns 422 when linked tag normalises to nico tag' do
+    it 'clears existing links and records the empty mapping for a member' do
       sign_in_as(member)
-
-      other_nico = create(:tag, :nico, name: 'nico:linked_ng')
-      TagName.create!(name: 'linked_ng_alias', canonical: other_nico.tag_name)
-
-      TagVersioning.ensure_snapshot!(nico_tag, created_by_user: member)
+      linked = create(:tag)
+      NicoTagRelation.insert_all!([{ nico_tag_id: nico_tag.id, tag_id: linked.id }])
+      NicoTagVersionRecorder.record!(external_tag: nico_tag,
+                                     event_type: :create, created_by_user: member)
 
       expect {
-        patch "/tags/nico/#{nico_tag.id}", params: { tags: 'linked_ng_alias' }
-      }.not_to change(NicoTagVersion, :count)
+        patch "/tags/nico/#{ nico_tag.id }", params: { tags: '' }
+      }.to change(NicoTagVersion, :count).by(1)
 
-      expect(response).to have_http_status(:unprocessable_entity)
-      expect(json.fetch('errors')).to include(
-          'tags' => ['ニコニコ・タグ同士は連携できません．'])
+      expect(response).to have_http_status(:ok)
+      expect(json).to eq([])
+      expect(nico_tag.reload.linked_tags).to be_empty
+      expect(nico_tag.nico_tag_versions.order(:version_no).last)
+          .to have_attributes(linked_tags: '', created_by_user: member)
     end
 
     it 'returns the tags field error when a nico tag is specified directly' do

backend/spec/requests/tag_children_spec.rb

@@ -80,38 +80,6 @@ RSpec.describe "TagChildren", type: :request do
         expect(response).to have_http_status(:not_found)
       end
     end
-
-    context 'when parent is nico' do
-      before { stub_current_user(admin) }
-
-      let!(:parent) { create(:tag, :nico, name: 'nico:parent_ng') }
-      let(:parent_id) { parent.id }
-      let(:child_id) { child.id }
-
-      it 'returns 400 and does not create relation' do
-        expect {
-          do_request
-        }.not_to change(TagImplication, :count)
-
-        expect(response).to have_http_status(:bad_request)
-      end
-    end
-
-    context 'when child is nico' do
-      before { stub_current_user(admin) }
-
-      let!(:child) { create(:tag, :nico, name: 'nico:child_ng') }
-      let(:parent_id) { parent.id }
-      let(:child_id) { child.id }
-
-      it 'returns 400 and does not create relation' do
-        expect {
-          do_request
-        }.not_to change(TagImplication, :count)
-
-        expect(response).to have_http_status(:bad_request)
-      end
-    end
   end
 
   describe "DELETE /tag_children" do
@@ -186,31 +154,5 @@ RSpec.describe "TagChildren", type: :request do
         expect(response).to have_http_status(:not_found)
       end
     end
-
-    context 'when parent is nico' do
-      before { stub_current_user(admin) }
-
-      let!(:parent) { create(:tag, :nico, name: 'nico:parent_ng_delete') }
-      let(:parent_id) { parent.id }
-      let(:child_id) { child.id }
-
-      it 'returns 400' do
-        do_request
-        expect(response).to have_http_status(:bad_request)
-      end
-    end
-
-    context 'when child is nico' do
-      before { stub_current_user(admin) }
-
-      let!(:child) { create(:tag, :nico, name: 'nico:child_ng_delete') }
-      let(:parent_id) { parent.id }
-      let(:child_id) { child.id }
-
-      it 'returns 400' do
-        do_request
-        expect(response).to have_http_status(:bad_request)
-      end
-    end
   end
 end

backend/spec/requests/tag_versions_spec.rb

@@ -3,13 +3,13 @@ require 'rails_helper'
 RSpec.describe 'TagVersions API', type: :request do
   let(:member) { create(:user, :member, name: 'version member') }
 
-  let!(:tag) { create(:tag, name: 'tag_versions_target', category: :general) }
-  let!(:other_tag) { create(:tag, name: 'tag_versions_other', category: :general) }
+  let!(:tag) { create(:tag, primary_name: 'tag_versions_target', category: :general) }
+  let!(:other_tag) { create(:tag, primary_name: 'tag_versions_other', category: :general) }
 
-  let!(:parent_shared) { create(:tag, name: 'parent_shared', category: :general) }
-  let!(:parent_old) { create(:tag, name: 'parent_old', category: :general) }
-  let!(:parent_new) { create(:tag, name: 'parent_new', category: :general) }
-  let!(:other_parent) { create(:tag, name: 'other_parent', category: :general) }
+  let!(:parent_shared) { create(:tag, primary_name: 'parent_shared', category: :general) }
+  let!(:parent_old) { create(:tag, primary_name: 'parent_old', category: :general) }
+  let!(:parent_new) { create(:tag, primary_name: 'parent_new', category: :general) }
+  let!(:other_parent) { create(:tag, primary_name: 'other_parent', category: :general) }
 
   let(:t_v1) { Time.zone.local(2020, 1, 1, 12, 0, 0) }
   let(:t_v2) { Time.zone.local(2020, 1, 2, 12, 0, 0) }
@@ -36,6 +36,10 @@ RSpec.describe 'TagVersions API', type: :request do
             category: category,
             deprecated_at: deprecated_at,
             aliases: Array(aliases).join(' '),
+            names: { ja: { name:, script_code: 'Jpan', auto_generated: false,
+                           aliases: Array(aliases).sort.map { |alias_name|
+                             { name: alias_name, script_code: 'Jpan' }
+                           } } },
             parent_tag_ids: Array(parent_tags).map(&:id).join(' '),
             created_by_user: created_by_user,
             created_at: created_at)
@@ -211,7 +215,7 @@ RSpec.describe 'TagVersions API', type: :request do
     end
 
     it 'returns empty when the specified tag has no versions' do
-      fresh_tag = create(:tag, name: 'no_versions_tag', category: :general)
+      fresh_tag = create(:tag, primary_name: 'no_versions_tag', category: :general)
 
       get '/tags/versions', params: { id: fresh_tag.id }
 
@@ -232,8 +236,8 @@ RSpec.describe 'TagVersions API', type: :request do
     end
 
     it 'does not create tag versions by wiki updates when tag has no versions yet' do
-      wiki_tag_name = TagName.create!(name: 'tag_versions_from_wiki')
-      wiki_tag = Tag.create!(tag_name: wiki_tag_name, category: :general)
+      wiki_tag_name = create(:tag_name, name: 'tag_versions_from_wiki')
+      wiki_tag = create(:tag, primary_tag_name: wiki_tag_name, category: :general)
 
       wiki_page =
           Wiki::Commit.create_content!(

backend/spec/requests/tag_wiki_history_integrity_spec.rb

@@ -8,13 +8,13 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
   end
 
   def create_tag! name:, category: :general
-    tag_name = TagName.create!(name:)
-    Tag.create!(tag_name:, category:)
+    tag_name = create(:tag_name, name:)
+    create(:tag, primary_tag_name: tag_name, category:)
   end
 
   def create_wiki_for_tag! tag:, body: 'wiki body', user: member_user
     Wiki::Commit.create_content!(
-        tag_name: tag.tag_name,
+        tag_name: primary_tag_name_for(tag, 'ja'),
         body:,
         created_by_user: user,
         message: 'init')
@@ -43,7 +43,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       wiki_page.reload
       version = wiki_page.wiki_versions.order(:version_no).last
 
-      expect(tag.name).to eq('patch_tag_wiki_after')
+      expect(primary_tag_name_for(tag, 'ja').name).to eq('patch_tag_wiki_after')
       expect(wiki_page.title).to eq('patch_tag_wiki_after')
 
       expect(version).to have_attributes(
@@ -72,7 +72,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       tag.reload
       wiki_page.reload
 
-      expect(tag.name).to eq('patch_tag_category_only')
+      expect(primary_tag_name_for(tag, 'ja').name).to eq('patch_tag_category_only')
       expect(tag.category).to eq('meme')
       expect(wiki_page.wiki_versions.count).to eq(before_wiki_versions)
     end
@@ -101,7 +101,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       wiki_page.reload
       version = wiki_page.wiki_versions.order(:version_no).last
 
-      expect(tag.name).to eq('put_tag_wiki_after')
+      expect(primary_tag_name_for(tag, 'ja').name).to eq('put_tag_wiki_after')
       expect(wiki_page.title).to eq('put_tag_wiki_after')
 
       expect(version).to have_attributes(
@@ -134,7 +134,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       tag.reload
       wiki_page.reload
 
-      expect(tag.name).to eq('put_tag_category_only')
+      expect(primary_tag_name_for(tag, 'ja').name).to eq('put_tag_category_only')
       expect(tag.category).to eq('meme')
       expect(wiki_page.wiki_versions.count).to eq(before_wiki_versions)
     end