diff --git a/backend/app/controllers/application_controller.rb b/backend/app/controllers/application_controller.rb
index 95ec17a..0023bd5 100644
--- a/backend/app/controllers/application_controller.rb
+++ b/backend/app/controllers/application_controller.rb
@@ -92,4 +92,6 @@ class ApplicationController < ActionController::API
 
     value
   end
+
+  def resolve_locale! = Locale.find_by(code: params[:locale]) || Locale.nipponese
 end
diff --git a/backend/app/controllers/deerjikists_controller.rb b/backend/app/controllers/deerjikists_controller.rb
index 9302370..e6cc209 100644
--- a/backend/app/controllers/deerjikists_controller.rb
+++ b/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
diff --git a/backend/app/controllers/gekanator_posts_controller.rb b/backend/app/controllers/gekanator_posts_controller.rb
index a176354..b8be760 100644
--- a/backend/app/controllers/gekanator_posts_controller.rb
+++ b/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
diff --git a/backend/app/controllers/gekanator_questions_controller.rb b/backend/app/controllers/gekanator_questions_controller.rb
index cc08a21..60e8725 100644
--- a/backend/app/controllers/gekanator_questions_controller.rb
+++ b/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|
diff --git a/backend/app/controllers/materials_controller.rb b/backend/app/controllers/materials_controller.rb
index e4ada01..f94f511 100644
--- a/backend/app/controllers/materials_controller.rb
+++ b/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_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? }
diff --git a/backend/app/controllers/nico_tags_controller.rb b/backend/app/controllers/nico_tags_controller.rb
index 6f97dbc..64f74ab 100644
--- a/backend/app/controllers/nico_tags_controller.rb
+++ b/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
@@ -24,7 +26,7 @@ class NicoTagsController < ApplicationController
         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_name: :wiki_page })
+        .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 ?"),
@@ -34,7 +36,8 @@ class NicoTagsController < ApplicationController
     if linked_tag
       linked_tag_ids =
           Tag
-          .joins(:tag_name)
+          .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)
@@ -67,7 +70,9 @@ class NicoTagsController < ApplicationController
     render json: { tags: tags.map { |tag|
       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
 
@@ -81,6 +86,8 @@ class NicoTagsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
+
     id = params[:id].to_i
 
     tag = ExternalTag.find(id)
@@ -89,10 +96,14 @@ class NicoTagsController < ApplicationController
     linked_tags = nil
 
     ApplicationRecord.transaction do
-      linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
-                                                          with_no_deerjikist: false)
+      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!
@@ -102,7 +113,9 @@ class NicoTagsController < ApplicationController
                                      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
diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index b9023b0..3843bb7 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/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
@@ -46,12 +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(:external_tags, :uploaded_user, :parents, :children,
                  post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                { tag_name: :wiki_page }] }])
+                                                { tag_names: :wiki_page }] }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -90,7 +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)
@@ -102,17 +105,19 @@ class PostsController < ApplicationController
   end
 
   def random
+    locale = resolve_locale!
+
     post =
-        filtered_posts
+        filtered_posts(locale)
         .preload(:uploaded_user, :parents, :children,
                  post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                { tag_name: :wiki_page }] }])
+                                                { 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
@@ -187,11 +192,13 @@ class PostsController < ApplicationController
   end
 
   def show
+    locale = resolve_locale!
+
     post =
         Post
         .includes(:uploaded_user, :parents, :children,
                   post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                 { tag_name: :wiki_page }] }])
+                                                 { tag_names: :wiki_page }] }])
         .with_attached_thumbnail
         .find_by(id: params[:id])
     return head :not_found unless post
@@ -205,18 +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])
@@ -242,10 +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
@@ -271,13 +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．'
@@ -310,6 +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]
@@ -329,9 +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:,
@@ -360,14 +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．'] }
@@ -385,19 +402,19 @@ class PostsController < ApplicationController
 
   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
 
@@ -405,11 +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
@@ -419,8 +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
@@ -428,11 +445,11 @@ class PostsController < ApplicationController
     end
   end
 
-  def tagged_post_ids_for(name)
+  def tagged_post_ids_for locale, name
     posts_by_internal_tags =
         Post
-        .joins(tags: :tag_name)
-        .where(tag_names: { name: })
+        .joins(tags: :tag_names)
+        .where(tag_names: { language_code: locale.language_code, name: })
         .select(:id)
 
     posts_by_external_tags =
@@ -474,7 +491,7 @@ class PostsController < ApplicationController
     end
   end
 
-  def build_tag_tree_for post
+  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)
@@ -504,7 +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)
@@ -516,7 +533,7 @@ 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
 
     internal_tags = root_ids.filter_map { |id| build_node.call(id, []) }
@@ -672,40 +689,46 @@ class PostsController < ApplicationController
     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
-        .joins(tag: :tag_name)
+        .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:)
@@ -716,7 +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
@@ -840,7 +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],
@@ -848,11 +871,12 @@ class PostsController < ApplicationController
                  original_created_from: snapshot[:original_created_from],
                  original_created_before: snapshot[:original_created_before])
 
-    Tag.normalise_tags!(snapshot[:tag_names],
+    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)
+    TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user,
+                                        language_code: locale.language_code)
 
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
 
diff --git a/backend/app/controllers/tag_versions_controller.rb b/backend/app/controllers/tag_versions_controller.rb
index 243a548..f45d042 100644
--- a/backend/app/controllers/tag_versions_controller.rb
+++ b/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
diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index dae8994..9be0365 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/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
@@ -36,9 +38,14 @@ class TagsController < ApplicationController
 
     tags =
         if post_id.present?
-          Tag.joins(:posts, :tag_name).where(posts: { id: post_id })
+          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
 
     external_tags =
@@ -167,9 +174,10 @@ class TagsController < ApplicationController
 
     tags_by_id =
         Tag
-        .joins(:tag_name)
-        .includes(:tag_name, :materials, tag_name: :wiki_page)
-        .where(id: tag_ids)
+        .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
@@ -178,7 +186,7 @@ class TagsController < ApplicationController
 
     render json: { tags: rows.map { |row|
       if row['source'] == 'tag'
-        TagRepr.base(tags_by_id.fetch(row['id']))
+        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
@@ -190,7 +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
@@ -205,6 +214,8 @@ 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) }%"
 
@@ -213,35 +224,36 @@ class TagsController < ApplicationController
 
     alias_rows =
         TagName
+        .where(language_code: locale.language_code, primary_flg: false)
         .where('name LIKE ?', prefix)
-        .where.not(canonical_id: nil)
-        .pluck(:canonical_id, :name)
+        .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)
+        .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('tag_names.name LIKE ?', prefix)
 
-    internal_tags = canonical_hit.or(base.where(tag_name_id: canonical_ids.uniq))
+    internal_tags = canonical_hit.or(base.where(id: tag_ids.uniq))
 
     internal_rows =
         internal_tags
         .order(Arel.sql('tags.post_count DESC, tag_names.name'))
         .limit(20)
         .map { |tag|
-          TagRepr.base(tag).merge(matched_alias: matched_alias_by_tag_name_id[tag.tag_name_id])
+          TagRepr.base(tag, language_code: locale.language_code)
+                 .merge(matched_alias: matched_alias_by_tag_id[tag.id])
         }
 
     return render json: internal_rows unless with_nico
@@ -257,20 +269,23 @@ class TagsController < ApplicationController
         .map { external_tag_json(_1) }
 
     rows =
-        (internal_rows + external_rows)
-        .sort_by { |row| [-row['post_count'], row['name']] }
+    (internal_rows + external_rows)
+        .sort_by { |row| [-row['post_count'], row['name'] || row[:name]] }
         .first(20)
 
     render json: rows
   end
 
   def show
+    locale = resolve_locale!
+
     tag =
         Tag
-        .joins(:tag_name)
-        .includes(:tag_name, :materials, tag_name: :wiki_page)
-        .find_by(id: params[:id])
-    return render json: TagRepr.base(tag) if 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
@@ -282,12 +297,14 @@ class TagsController < ApplicationController
     name = params[:name].to_s.strip
     return render_bad_request('name は必須です．') if name.blank?
 
+    locale = resolve_locale!
+
     tag =
         Tag
-        .joins(:tag_name)
-        .includes(:tag_name, :materials, tag_name: :wiki_page)
-        .find_by(tag_names: { name: })
-    return render json: TagRepr.base(tag) if 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
@@ -299,35 +316,52 @@ class TagsController < ApplicationController
   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)
@@ -346,7 +380,7 @@ class TagsController < ApplicationController
         row_indexes_by_key.key?([deerjikist.platform, deerjikist.code])
       }
 
-      render_deerjikist_conflicts(requested_deerjikists, row_indexes_by_key, tag)
+      render_deerjikist_conflicts(locale, requested_deerjikists, row_indexes_by_key, tag)
       raise ActiveRecord::Rollback if performed?
 
       requested_keys_set = requested_keys.to_set
@@ -367,7 +401,7 @@ class TagsController < ApplicationController
           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(conflicts, row_indexes_by_key, tag)
+          render_deerjikist_conflicts(locale, conflicts, row_indexes_by_key, tag)
         end
         raise ActiveRecord::Rollback if performed?
       end
@@ -375,22 +409,28 @@ class TagsController < ApplicationController
 
     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
@@ -406,7 +446,9 @@ 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
@@ -417,24 +459,25 @@ class TagsController < ApplicationController
     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
 
@@ -442,17 +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)
@@ -460,20 +506,21 @@ class TagsController < ApplicationController
 
     tag = Tag.find(params[:id])
 
-    return unless validate_tag_rename(tag, name)
+    return unless validate_tag_rename(locale, tag, name)
 
     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)
@@ -485,11 +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
@@ -501,7 +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] = [] }
 
@@ -516,10 +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
@@ -651,29 +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
-    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!(
@@ -682,30 +737,43 @@ 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.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.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
 
@@ -713,72 +781,96 @@ class TagsController < ApplicationController
   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.update!(canonical: nil)
+    current_tag_name.wiki_page&.update!(tag_name_id: promoted_tag_name.id)
+    current_tag_name.association(:wiki_page).reset
 
-    TagName.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_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_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)
+  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
 
@@ -851,15 +943,17 @@ class TagsController < ApplicationController
       .to_a
   end
 
-  def render_deerjikist_conflicts deerjikists, row_indexes_by_key, tag
+  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_name)
-                      .where(id: conflicts.map(&:tag_id).uniq)
-                      .pluck('tags.id', 'tag_names.name')
-                      .to_h
+    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|
diff --git a/backend/app/controllers/theatre_skip_events_controller.rb b/backend/app/controllers/theatre_skip_events_controller.rb
index fbbdae9..c5047c5 100644
--- a/backend/app/controllers/theatre_skip_events_controller.rb
+++ b/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 }
     }
diff --git a/backend/app/controllers/wiki_pages_controller.rb b/backend/app/controllers/wiki_pages_controller.rb
index 9b38b0e..b0d0b8c 100644
--- a/backend/app/controllers/wiki_pages_controller.rb
+++ b/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_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!(
diff --git a/backend/app/models/external_tag.rb b/backend/app/models/external_tag.rb
index f49ec54..dc81bef 100644
--- a/backend/app/models/external_tag.rb
+++ b/backend/app/models/external_tag.rb
@@ -14,7 +14,11 @@ class ExternalTag < ApplicationRecord
 
   has_many :linked_tags, through: :nico_tag_relations, source: :tag
 
-  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 = 'ja'
+    linked_tags
+        .joins(:tag_names)
+        .where(tag_names: { language_code:, primary_flg: true })
+        .order('tag_names.name')
+        .pluck('tag_names.name')
   end
 end
diff --git a/backend/app/models/language.rb b/backend/app/models/language.rb
new file mode 100644
index 0000000..fb2727f
--- /dev/null
+++ b/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
diff --git a/backend/app/models/locale.rb b/backend/app/models/locale.rb
new file mode 100644
index 0000000..1d39f44
--- /dev/null
+++ b/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
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 805e91d..6db6ca8 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -126,13 +126,14 @@ class Post < ApplicationRecord
     super(options).merge(thumbnail: nil)
   end
 
-  def snapshot_tag_names
+  def snapshot_tag_names language_code = 'ja'
     post_tags
-        .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?
@@ -152,16 +153,17 @@ class Post < ApplicationRecord
     "#{ tag.fetch('name') }#{ sections.join }"
   end
 
-  def snapshot_tags_json
+  def snapshot_tags_json language_code = 'ja'
     tag_snapshots =
         post_tags
-            .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('tags.id')
             .map { |pt|
           { 'tag_id' => pt.tag.id,
             'version_no' => pt.tag.version_no,
-            'name' => pt.tag.name,
+            '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 }
diff --git a/backend/app/models/region.rb b/backend/app/models/region.rb
new file mode 100644
index 0000000..85476d6
--- /dev/null
+++ b/backend/app/models/region.rb
@@ -0,0 +1,3 @@
+class Region < ApplicationRecord
+  ;
+end
diff --git a/backend/app/models/script.rb b/backend/app/models/script.rb
new file mode 100644
index 0000000..bbc23f1
--- /dev/null
+++ b/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
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 02346d4..7891029 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -50,14 +50,10 @@ class Tag < ApplicationRecord
 
   has_many :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',
@@ -67,9 +63,8 @@ class Tag < ApplicationRecord
 
   validates :category, presence: true, inclusion: { in: Tag.categories.keys }
 
-  validate :tag_name_mustnt_start_with_nico
-  validate :tag_name_must_be_canonical
   validate :category_must_be_deerjikist_with_deerjikists
+  validate :tag_names_must_be_valid
 
   CATEGORY_PREFIXES = {
       'general:'    => :general,
@@ -83,8 +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?
@@ -95,214 +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_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(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_or_create_by!(name: name.to_s.strip)
-    tn = tn.canonical if tn.canonical_id?
-
-    Tag.find_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.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
-
-        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.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 snapshot_aliases = tag_name.aliases.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 tag_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
+  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
 
@@ -311,30 +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
 end
diff --git a/backend/app/models/tag_name.rb b/backend/app/models/tag_name.rb
index fe12a06..6c119ab 100644
--- a/backend/app/models/tag_name.rb
+++ b/backend/app/models/tag_name.rb
@@ -1,43 +1,61 @@
 class TagName < ApplicationRecord
-  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
 
@@ -46,4 +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
diff --git a/backend/app/models/tag_name_sanitisation_rule.rb b/backend/app/models/tag_name_sanitisation_rule.rb
index 37cde5f..4731d4f 100644
--- a/backend/app/models/tag_name_sanitisation_rule.rb
+++ b/backend/app/models/tag_name_sanitisation_rule.rb
@@ -15,31 +15,39 @@ class TagNameSanitisationRule < ApplicationRecord
     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.destroy!
 
-            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
diff --git a/backend/app/models/tag_version.rb b/backend/app/models/tag_version.rb
index 6ca5d0a..8b6e31a 100644
--- a/backend/app/models/tag_version.rb
+++ b/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
diff --git a/backend/app/representations/deerjikist_repr.rb b/backend/app/representations/deerjikist_repr.rb
index fbb73c9..dbe8fb8 100644
--- a/backend/app/representations/deerjikist_repr.rb
+++ b/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
diff --git a/backend/app/representations/material_repr.rb b/backend/app/representations/material_repr.rb
index 30d21f9..0482569 100644
--- a/backend/app/representations/material_repr.rb
+++ b/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
diff --git a/backend/app/representations/post_repr.rb b/backend/app/representations/post_repr.rb
index 01206e4..4784526 100644
--- a/backend/app/representations/post_repr.rb
+++ b/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|
@@ -86,14 +86,14 @@ module PostRepr
                        end)
   end
 
-  def tag_json post
+  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(
+          TagRepr.inline(post_tag.tag, language_code:).merge(
               'children' => [],
               'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
         }
diff --git a/backend/app/representations/tag_repr.rb b/backend/app/representations/tag_repr.rb
index 3958953..9e3a42e 100644
--- a/backend/app/representations/tag_repr.rb
+++ b/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
diff --git a/backend/app/services/material_version_recorder.rb b/backend/app/services/material_version_recorder.rb
index 8f268f7..08d5ad1 100644
--- a/backend/app/services/material_version_recorder.rb
+++ b/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,
diff --git a/backend/app/services/post_bulk_creator.rb b/backend/app/services/post_bulk_creator.rb
index 1e75e24..38ec06e 100644
--- a/backend/app/services/post_bulk_creator.rb
+++ b/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 } }
diff --git a/backend/app/services/post_create_plan.rb b/backend/app/services/post_create_plan.rb
index fedd574..58fbaf2 100644
--- a/backend/app/services/post_create_plan.rb
+++ b/backend/app/services/post_create_plan.rb
@@ -8,13 +8,13 @@ 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
@@ -42,14 +42,16 @@ class PostCreatePlan
 
   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::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,
@@ -65,7 +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 {
@@ -74,7 +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?
 
@@ -87,17 +89,17 @@ class PostCreatePlan
       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
@@ -131,13 +134,15 @@ 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,
+             { name: tag.name(locale.language_code),
                category: tag.category.to_sym }
         }
     merge_tag_specs(snapshot_tag_specs + expanded_parent_specs)
@@ -156,33 +161,37 @@ class PostCreatePlan
     }.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
diff --git a/backend/app/services/post_create_preflight.rb b/backend/app/services/post_create_preflight.rb
index 04d3492..c27fc3c 100644
--- a/backend/app/services/post_create_preflight.rb
+++ b/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],
diff --git a/backend/app/services/post_creator.rb b/backend/app/services/post_creator.rb
index 788a671..fe3e6a1 100644
--- a/backend/app/services/post_creator.rb
+++ b/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|
diff --git a/backend/app/services/post_import_previewer.rb b/backend/app/services/post_import_previewer.rb
index 0a812f5..2431ded 100644
--- a/backend/app/services/post_import_previewer.rb
+++ b/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)
@@ -346,7 +348,7 @@ class PostImportPreviewer
     { 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．']
diff --git a/backend/app/services/post_metadata_fetcher.rb b/backend/app/services/post_metadata_fetcher.rb
index a8dcb6d..c5e2eaf 100644
--- a/backend/app/services/post_metadata_fetcher.rb
+++ b/backend/app/services/post_metadata_fetcher.rb
@@ -47,9 +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]
diff --git a/backend/app/services/tag_version_recorder.rb b/backend/app/services/tag_version_recorder.rb
index a786058..e14d497 100644
--- a/backend/app/services/tag_version_recorder.rb
+++ b/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
diff --git a/backend/app/services/tag_versioning.rb b/backend/app/services/tag_versioning.rb
index d874a3e..4990801 100644
--- a/backend/app/services/tag_versioning.rb
+++ b/backend/app/services/tag_versioning.rb
@@ -1,22 +1,22 @@
 class TagVersioning
-  def self.record! tag, event_type:, created_by_user:
-    TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+  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:
+  def self.ensure_snapshot! tag, created_by_user:, language_code: 'ja'
     return if tag.tag_versions.exists?
 
-    TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
+    TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:, language_code:)
   end
 
-  def self.record_tag_snapshot! tag, 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:)
+    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
diff --git a/backend/app/services/theatre_post_selector.rb b/backend/app/services/theatre_post_selector.rb
index 124c913..8d5ab32 100644
--- a/backend/app/services/theatre_post_selector.rb
+++ b/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
diff --git a/backend/db/migrate/20260922000000_create_languages.rb b/backend/db/migrate/20260922000000_create_languages.rb
new file mode 100644
index 0000000..e9f1887
--- /dev/null
+++ b/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
diff --git a/backend/db/migrate/20260922010000_create_scripts.rb b/backend/db/migrate/20260922010000_create_scripts.rb
new file mode 100644
index 0000000..b825c84
--- /dev/null
+++ b/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}$', 'c')",
+                         name: 'scripts_code_check'
+    end
+
+    execute <<~SQL
+      INSERT INTO
+        scripts(code, name, created_at)
+      VALUES
+        ('Jpan', '漢字、仮名文字およびラテン文字', #{ connection.quote Time.current })
+    SQL
+  end
+
+  def down
+    drop_table :scripts
+  end
+end
diff --git a/backend/db/migrate/20260922013000_create_regions.rb b/backend/db/migrate/20260922013000_create_regions.rb
new file mode 100644
index 0000000..c44c069
--- /dev/null
+++ b/backend/db/migrate/20260922013000_create_regions.rb
@@ -0,0 +1,25 @@
+class CreateRegions < ActiveRecord::Migration[8.0]
+  def up
+    create_table :regions, id: { type: :integer, limit: 2 }, primary_key: :code do |t|
+      t.column :alpha_code, 'CHAR(2)'
+      t.string :name, null: false
+      t.datetime :deprecated_at, index: true
+      t.datetime :created_at, null: false
+
+      t.check_constraint "REGEXP_LIKE(alpha_code, '^[A-Z]{2}$', '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
diff --git a/backend/db/migrate/20260922020000_create_locales.rb b/backend/db/migrate/20260922020000_create_locales.rb
new file mode 100644
index 0000000..c396b69
--- /dev/null
+++ b/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
diff --git a/backend/db/migrate/20260922030000_add_columns_to_tag_names.rb b/backend/db/migrate/20260922030000_add_columns_to_tag_names.rb
new file mode 100644
index 0000000..0924d82
--- /dev/null
+++ b/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
diff --git a/backend/db/migrate/20260922040000_add_names_to_tag_versions.rb b/backend/db/migrate/20260922040000_add_names_to_tag_versions.rb
new file mode 100644
index 0000000..817b6d4
--- /dev/null
+++ b/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
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index c4ce56a..eee4568 100644
--- a/backend/db/schema.rb
+++ b/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_09_21_230000) 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
@@ -138,6 +138,29 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_230000) 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
@@ -388,6 +411,24 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_230000) 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
@@ -420,12 +461,22 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_230000) 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.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 ["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|
@@ -447,11 +498,13 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_230000) 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|
@@ -701,6 +754,9 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_230000) 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"
@@ -734,7 +790,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_230000) do
   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", "users", column: "created_by_user_id"
diff --git a/backend/spec/db/delete_discarded_tags_spec.rb b/backend/spec/db/delete_discarded_tags_spec.rb
index 3882e0d..6d6a533 100644
--- a/backend/spec/db/delete_discarded_tags_spec.rb
+++ b/backend/spec/db/delete_discarded_tags_spec.rb
@@ -11,6 +11,7 @@ RSpec.describe 'discarded tag cleanup migrations' do
   end
 
   context 'with legacy records' do
+    # Reproduce the historical schema required by these pre-multilingual migrations.
     self.use_transactional_tests = false
 
     before do
diff --git a/backend/spec/db/tag_name_constraints_spec.rb b/backend/spec/db/tag_name_constraints_spec.rb
new file mode 100644
index 0000000..02ba449
--- /dev/null
+++ b/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
diff --git a/backend/spec/db/tag_version_names_spec.rb b/backend/spec/db/tag_version_names_spec.rb
new file mode 100644
index 0000000..3c351b4
--- /dev/null
+++ b/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
diff --git a/backend/spec/factories/tag_names.rb b/backend/spec/factories/tag_names.rb
index a33be1e..0e98e3b 100644
--- a/backend/spec/factories/tag_names.rb
+++ b/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
diff --git a/backend/spec/factories/tags.rb b/backend/spec/factories/tags.rb
index 55db316..d4ac59b 100644
--- a/backend/spec/factories/tags.rb
+++ b/backend/spec/factories/tags.rb
@@ -1,15 +1,41 @@
 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
+
+    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
 end
diff --git a/backend/spec/models/language_spec.rb b/backend/spec/models/language_spec.rb
new file mode 100644
index 0000000..9a2edcb
--- /dev/null
+++ b/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
diff --git a/backend/spec/models/locale_spec.rb b/backend/spec/models/locale_spec.rb
new file mode 100644
index 0000000..62fbd55
--- /dev/null
+++ b/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
diff --git a/backend/spec/models/material_export_item_spec.rb b/backend/spec/models/material_export_item_spec.rb
index d98e225..19734a0 100644
--- a/backend/spec/models/material_export_item_spec.rb
+++ b/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)
diff --git a/backend/spec/models/post_spec.rb b/backend/spec/models/post_spec.rb
index ea5646e..f12d90b 100644
--- a/backend/spec/models/post_spec.rb
+++ b/backend/spec/models/post_spec.rb
@@ -18,7 +18,7 @@ RSpec.describe Post, type: :model do
       expect(post.snapshot_tags_json).to eq([
           { 'tag_id' => tag.id,
             'version_no' => tag.version_no,
-            'name' => tag.name,
+            'name' => primary_tag_name_for(tag, 'ja').name,
             'category' => tag.category,
             'sections' => [{ 'begin_ms' => 2000, 'end_ms' => nil }] },
           { 'external_tag_id' => external.id }])
diff --git a/backend/spec/models/post_version_spec.rb b/backend/spec/models/post_version_spec.rb
index 4cc0e82..f29b530 100644
--- a/backend/spec/models/post_version_spec.rb
+++ b/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|
diff --git a/backend/spec/models/script_spec.rb b/backend/spec/models/script_spec.rb
new file mode 100644
index 0000000..20365c1
--- /dev/null
+++ b/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
diff --git a/backend/spec/models/tag_implication_spec.rb b/backend/spec/models/tag_implication_spec.rb
index a29cc1c..9034d2e 100644
--- a/backend/spec/models/tag_implication_spec.rb
+++ b/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!(
diff --git a/backend/spec/models/tag_name_sanitisation_rule_spec.rb b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
index b82f9fa..9cebc51 100644
--- a/backend/spec/models/tag_name_sanitisation_rule_spec.rb
+++ b/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
@@ -47,10 +83,10 @@ 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
@@ -63,48 +99,56 @@ RSpec.describe TagNameSanitisationRule, type: :model do
     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(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
-        TagName.create!(name: 'foobar', canonical: existing_tag.tag_name)
+        create(:tag_name, :alias, name: 'foobar', tag: existing_tag)
       end
       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 only the source and preserves the alias and its canonical tag' do
+      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.canonical).to eq(existing_tag.tag_name)
+        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
@@ -120,7 +164,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
         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(existing_tag.reload.name).to eq('foobar')
+        expect(primary_tag_name_for(existing_tag.reload, 'ja').name).to eq('foobar')
       end
     end
   end
diff --git a/backend/spec/models/tag_name_spec.rb b/backend/spec/models/tag_name_spec.rb
new file mode 100644
index 0000000..8239d65
--- /dev/null
+++ b/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
diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index d63be45..1d08b42 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -4,12 +4,12 @@ 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, name:)
+        tag = build(:tag, primary_name: name)
 
         expect(tag).to be_invalid
         expect(tag.errors[:name]).to be_present
         expect {
-          described_class.normalise_tags!([name])
+          described_class.normalise_tags!(Locale.nipponese, [name])
         }.to raise_error(Tag::NicoTagNormalisationError)
       end
     end
@@ -25,128 +25,161 @@ RSpec.describe Tag, type: :model do
   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)
@@ -163,8 +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!(
@@ -183,55 +216,268 @@ RSpec.describe Tag, type: :model do
   end
 
   describe '.find_or_create_by_tag_name!' do
+    context 'with an explicit locale' do
+      include_context 'English locale'
+
+      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!(
+        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(tag.name).to eq('lookup_new')
+      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 'reuses the canonical tag for an alias without changing its category' do
+    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)
-      alias_name = TagName.create!(name: 'lookup_alias', canonical: tag.tag_name)
+      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!(
+        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 'creates a tag for an existing canonical name reached through an alias' do
-      canonical = create(:tag_name)
-      alias_name = TagName.create!(name: 'lookup_alias', canonical:)
-      tag = nil
+    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 {
-        tag = described_class.find_or_create_by_tag_name!(
+        found = described_class.find_or_create_by_tag_name!(Locale.nipponese,
             alias_name.name, category: :general)
-      }.to change(Tag, :count).by(1).and change(TagName, :count).by(0)
+        expect(found).to eq(tag)
+      }.to change(Tag, :count).by(0).and change(TagName, :count).by(0)
 
-      expect(tag.tag_name).to eq(canonical)
+      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) }
 
@@ -243,7 +489,8 @@ RSpec.describe Tag, type: :model do
         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.canonical_id).to eq(target_tag.tag_name_id)
+        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
@@ -269,15 +516,16 @@ RSpec.describe Tag, type: :model do
         expect(target_post_tag.reload.sections).to contain_exactly(target_section)
 
         expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        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 = source_tag.name
-      source_alias = TagName.create!(name: 'merge_alias', canonical: source_tag_name)
+      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
 
@@ -287,13 +535,17 @@ RSpec.describe Tag, type: :model do
       expect(versions.pluck(:version_no, :event_type))
           .to eq([[1, 'create'], [2, 'discard']])
       expect(versions.first).to eq(original_version)
-      expect(versions.last).to have_attributes(
-          name: source_name, aliases: source_alias.name, created_by_user: user)
+      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'])
-      expect(target_versions.last.aliases.split).to eq([source_name])
+      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
@@ -347,7 +599,8 @@ RSpec.describe Tag, type: :model do
         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.canonical_id).to eq(target_tag.tag_name_id)
+        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
@@ -378,7 +631,8 @@ RSpec.describe Tag, type: :model do
         expect(target_link).to be_present
 
         expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        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
@@ -397,7 +651,7 @@ RSpec.describe Tag, type: :model do
 
       it 'rolls back earlier deletions, links, and history when a later source has a wiki' do
         earlier_source = create(:tag)
-        earlier_name = earlier_source.tag_name
+        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)
@@ -407,7 +661,8 @@ RSpec.describe Tag, type: :model do
         }.to raise_error(ActiveRecord::RecordInvalid)
 
         expect(Tag.unscoped.exists?(earlier_source.id)).to be(true)
-        expect(earlier_name.reload.canonical_id).to be_nil
+        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)
@@ -416,7 +671,8 @@ RSpec.describe Tag, type: :model do
         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.canonical_id).to be_nil
+        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
diff --git a/backend/spec/models/version_record_spec.rb b/backend/spec/models/version_record_spec.rb
index e76f4e7..561c19b 100644
--- a/backend/spec/models/version_record_spec.rb
+++ b/backend/spec/models/version_record_spec.rb
@@ -1,7 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe VersionRecord, type: :model do
-  let!(:tag) { create(:tag, name: '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
@@ -9,13 +9,14 @@ 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.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!
diff --git a/backend/spec/requests/deerjikists_spec.rb b/backend/spec/requests/deerjikists_spec.rb
index 136fc2d..8d26658 100644
--- a/backend/spec/requests/deerjikists_spec.rb
+++ b/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
 
diff --git a/backend/spec/requests/error_responses_spec.rb b/backend/spec/requests/error_responses_spec.rb
index a7b5191..81c3ab9 100644
--- a/backend/spec/requests/error_responses_spec.rb
+++ b/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' }
diff --git a/backend/spec/requests/gekanator_learning_spec.rb b/backend/spec/requests/gekanator_learning_spec.rb
index 26f271b..7154683 100644
--- a/backend/spec/requests/gekanator_learning_spec.rb
+++ b/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
         )
diff --git a/backend/spec/requests/gekanator_posts_spec.rb b/backend/spec/requests/gekanator_posts_spec.rb
index b21e414..8cfa46f 100644
--- a/backend/spec/requests/gekanator_posts_spec.rb
+++ b/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')
 
diff --git a/backend/spec/requests/locale_write_paths_spec.rb b/backend/spec/requests/locale_write_paths_spec.rb
new file mode 100644
index 0000000..48f2ed1
--- /dev/null
+++ b/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
diff --git a/backend/spec/requests/materials_spec.rb b/backend/spec/requests/materials_spec.rb
index c1ffdf4..14b5d8a 100644
--- a/backend/spec/requests/materials_spec.rb
+++ b/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'))
diff --git a/backend/spec/requests/nico_tags_spec.rb b/backend/spec/requests/nico_tags_spec.rb
index 243cbd3..50fdd0d 100644
--- a/backend/spec/requests/nico_tags_spec.rb
+++ b/backend/spec/requests/nico_tags_spec.rb
@@ -44,10 +44,10 @@ RSpec.describe 'NicoTags', type: :request do
       unlinked.update!(name: 'search_unlinked')
       other = create(:external_tag)
       other.update!(name: 'other')
-      destination = create(:tag, :general)
-      destination.tag_name.update!(name: 'destination_search')
+      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_',
@@ -151,7 +151,7 @@ RSpec.describe 'NicoTags', type: :request 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(:not_found)
@@ -162,18 +162,18 @@ RSpec.describe 'NicoTags', type: :request do
 
       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)
 
       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)
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 8660634..38bc115 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -113,8 +113,8 @@ RSpec.describe 'Posts API', type: :request do
         'sections' => [])
   end
 
-  let!(:tag_name) { TagName.create!(name: 'spec_tag') }
-  let!(:tag)      { Tag.create!(tag_name: tag_name, category: :general) }
+  let!(:tag_name) { create(:tag_name, name: '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/spec').tap do |p|
@@ -125,11 +125,11 @@ RSpec.describe 'Posts API', type: :request do
   describe 'GET /posts' do
     let!(:user) { create_member_user! }
 
-    let!(:tag_name) { TagName.create!(name: 'spec_tag') }
-    let!(:tag) { Tag.create!(tag_name:, category: :general) }
-    let!(:tag_name2) { TagName.create!(name: 'unko') }
-    let!(:tag2) { Tag.create!(tag_name: tag_name2, category: :deerjikist) }
-    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
+    let!(:tag_name) { create(:tag_name, name: 'spec_tag') }
+    let!(:tag) { create(:tag, primary_tag_name: tag_name, category: :general) }
+    let!(:tag_name2) { create(:tag_name, name: 'unko') }
+    let!(:tag2) { create(:tag, primary_tag_name: tag_name2, category: :deerjikist) }
+    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', tag:) }
 
     let!(:hit_post) do
       Post.create!(uploaded_user: user, title: 'hello spec world',
@@ -267,7 +267,7 @@ RSpec.describe 'Posts API', type: :request do
       end
 
       it 'keeps internal name searches independent of colliding external ids' do
-        get '/posts', params: { tags: tag.name }
+        get '/posts', params: { tags: primary_tag_name_for(tag, 'ja').name }
 
         expect(response).to have_http_status(:ok)
         expect(json.fetch('count')).to eq(3)
@@ -286,7 +286,7 @@ RSpec.describe 'Posts API', type: :request do
 
       [nil, 'all'].each do |match|
         it "intersects internal and external matches with match=#{ match || 'omitted' }" do
-          params = { tags: "#{ tag.name } nico:search_external" }
+          params = { tags: "#{ primary_tag_name_for(tag, 'ja').name } nico:search_external" }
           params[:match] = match if match
 
           get '/posts', params: params
@@ -307,7 +307,8 @@ RSpec.describe 'Posts API', type: :request do
       end
 
       it 'excludes external matches from an internal tag search' do
-        get '/posts', params: { tags: "#{ tag.name } not:nico:search_external" }
+        get '/posts', params: {
+            tags: "#{ primary_tag_name_for(tag, 'ja').name } not:nico:search_external" }
 
         expect(response).to have_http_status(:ok)
         expect(json.fetch('count')).to eq(2)
@@ -316,7 +317,9 @@ RSpec.describe 'Posts API', type: :request do
       end
 
       it 'unions an external match with a negated internal match' do
-        get '/posts', params: { tags: "nico:search_external not:#{ tag.name }", match: 'any' }
+        get '/posts', params: {
+            tags: "nico:search_external not:#{ primary_tag_name_for(tag, 'ja').name }",
+            match: 'any' }
 
         expect(response).to have_http_status(:ok)
         expect(json.fetch('count')).to eq(2)
@@ -333,7 +336,9 @@ RSpec.describe 'Posts API', type: :request do
       end
 
       it 'applies the same mixed name search to the existing random endpoint' do
-        get '/posts/random', params: { tags: "#{ tag.name } nico:search_external", match: 'all' }
+        get '/posts/random', params: {
+            tags: "#{ primary_tag_name_for(tag, 'ja').name } nico:search_external",
+            match: 'all' }
 
         expect(response).to have_http_status(:ok)
         expect(json.fetch('id')).to eq(both_post.id)
@@ -341,17 +346,17 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     context 'when tags contain not:' do
-      let!(:foo_tag_name) { TagName.create!(name: 'not_spec_foo') }
-      let!(:foo_tag) { Tag.create!(tag_name: foo_tag_name, category: :general) }
+      let!(:foo_tag_name) { create(:tag_name, name: 'not_spec_foo') }
+      let!(:foo_tag) { create(:tag, primary_tag_name: foo_tag_name, category: :general) }
 
-      let!(:bar_tag_name) { TagName.create!(name: 'not_spec_bar') }
-      let!(:bar_tag) { Tag.create!(tag_name: bar_tag_name, category: :general) }
+      let!(:bar_tag_name) { create(:tag_name, name: 'not_spec_bar') }
+      let!(:bar_tag) { create(:tag, primary_tag_name: bar_tag_name, category: :general) }
 
-      let!(:baz_tag_name) { TagName.create!(name: 'not_spec_baz') }
-      let!(:baz_tag) { Tag.create!(tag_name: baz_tag_name, category: :general) }
+      let!(:baz_tag_name) { create(:tag_name, name: 'not_spec_baz') }
+      let!(:baz_tag) { create(:tag, primary_tag_name: baz_tag_name, category: :general) }
 
       let!(:foo_alias_tag_name) do
-        TagName.create!(name: 'not_spec_foo_alias', canonical: foo_tag_name)
+        create(:tag_name, :alias, name: 'not_spec_foo_alias', tag: foo_tag)
       end
 
       let!(:foo_only_post) do
@@ -739,7 +744,9 @@ RSpec.describe 'Posts API', type: :request do
           .find { _1['name'] == 'nico:post_index_external' }
 
       expect(post_json.fetch('tags')).to include(
-          a_hash_including('id' => tag.id, 'name' => tag.name, 'category' => 'general'))
+          a_hash_including('id' => tag.id,
+                           'name' => primary_tag_name_for(tag, 'ja').name,
+                           'category' => 'general'))
       expect(external_json).not_to be_nil
       expect_external_tag_json(external_json, external_tag)
     end
@@ -772,11 +779,10 @@ RSpec.describe 'Posts API', type: :request do
       end
 
       it 'omits deprecated tags' do
-        deprecated_tag = Tag.create!(
-          name: 'deprecated_post_tag',
-          category: :general,
-          deprecated_at: Time.current
-        )
+        deprecated_tag = create(:tag,
+            primary_name: 'deprecated_post_tag',
+            category: :general,
+            deprecated_at: Time.current)
         PostTag.create!(post: post_record, tag: deprecated_tag)
 
         request
@@ -853,9 +859,9 @@ RSpec.describe 'Posts API', type: :request do
 
         tags =
             15.times.map do |i|
-              tag_name = TagName.create!(name: "show_query_tag_#{ i }")
-              tag = Tag.create!(tag_name:, category: :general)
-              TagName.create!(name: "show_query_alias_#{ i }", canonical: tag_name)
+              tag_name = create(:tag_name, name: "show_query_tag_#{ i }")
+              tag = create(:tag, primary_tag_name: tag_name, category: :general)
+              create(:tag_name, :alias, name: "show_query_alias_#{ i }", tag:)
               PostTag.create!(post: post_record, tag:)
               tag
             end
@@ -910,7 +916,9 @@ RSpec.describe 'Posts API', type: :request do
         expect(response).to have_http_status(:ok)
 
         expect(json.fetch('tags')).to include(
-            a_hash_including('id' => tag.id, 'name' => tag.name, 'category' => 'general'))
+            a_hash_including('id' => tag.id,
+                             'name' => primary_tag_name_for(tag, 'ja').name,
+                             'category' => 'general'))
         external_json =
             json
             .fetch('tags')
@@ -1000,7 +1008,7 @@ RSpec.describe 'Posts API', type: :request do
 
   describe 'POST /posts' do
     let(:member) { create(:user, :member) }
-    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
+    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', tag:) }
 
     it '401 when not logged in' do
       sign_out
@@ -1157,11 +1165,10 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     it 'rejects a deprecated tag specified directly' do
-      Tag.create!(
-        name: 'deprecated_direct_tag',
-        category: :general,
-        deprecated_at: Time.current
-      )
+      create(:tag,
+          primary_name: 'deprecated_direct_tag',
+          category: :general,
+          deprecated_at: Time.current)
       sign_in_as(member)
 
       post '/posts', params: post_write_params(
@@ -1178,18 +1185,16 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     it 'expands through multiple deprecated parent tags and saves active ancestors' do
-      child = Tag.create!(name: 'active_child', category: :general)
-      deprecated_parent = Tag.create!(
-        name: 'deprecated_parent',
-        category: :general,
-        deprecated_at: Time.current
-      )
-      deprecated_grandparent = Tag.create!(
-        name: 'deprecated_grandparent',
-        category: :general,
-        deprecated_at: Time.current
-      )
-      active_grandparent = Tag.create!(name: 'active_grandparent', category: :general)
+      child = create(:tag, primary_name: 'active_child', category: :general)
+      deprecated_parent = create(:tag,
+          primary_name: 'deprecated_parent',
+          category: :general,
+          deprecated_at: Time.current)
+      deprecated_grandparent = create(:tag,
+          primary_name: 'deprecated_grandparent',
+          category: :general,
+          deprecated_at: Time.current)
+      active_grandparent = create(:tag, primary_name: 'active_grandparent', category: :general)
       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_grandparent)
@@ -1203,7 +1208,8 @@ RSpec.describe 'Posts API', type: :request do
       )
 
       expect(response).to have_http_status(:created)
-      saved_names = Post.find(json.fetch('id')).tags.map(&:name)
+      saved_names = TagName.where(tag_id: Post.find(json.fetch('id')).tags.select(:id),
+                                  language_code: 'ja', primary_flg: true).pluck(:name)
       expect(saved_names).to include('active_child', 'active_grandparent')
       expect(saved_names).not_to include('deprecated_parent', 'deprecated_grandparent')
     end
@@ -1306,7 +1312,8 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:created)
 
       created_post = Post.find(json.fetch('id'))
-      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      tag = TagName.find_by!(name: '伊地知ニジカ',
+                             language_code: 'ja', primary_flg: true).tag
       section = PostTagSection.find_by!(post: created_post, tag:)
 
       expect(section.begin_ms).to eq(60_000)
@@ -1326,7 +1333,8 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:created)
 
       created_post = Post.find(json.fetch('id'))
-      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      tag = TagName.find_by!(name: '伊地知ニジカ',
+                             language_code: 'ja', primary_flg: true).tag
       expect(PostTagSection.find_by(post: created_post, tag:)).to be_nil
     end
 
@@ -1343,7 +1351,8 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:created)
 
       created_post = Post.find(json.fetch('id'))
-      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      tag = TagName.find_by!(name: '伊地知ニジカ',
+                             language_code: 'ja', primary_flg: true).tag
       expect(PostTagSection.find_by(post: created_post, tag:)).to be_nil
     end
 
@@ -1622,6 +1631,7 @@ RSpec.describe 'Posts API', type: :request do
         expect(arguments[:thumbnails].keys).to eq([0])
         expect(arguments[:host]).to eq('http://www.example.com')
       end
+      expect(creator).to have_received(:run).with(Locale.nipponese)
     end
 
     it 'rejects malformed manifests as a request-level error' do
@@ -1658,8 +1668,8 @@ RSpec.describe 'Posts API', type: :request do
       create(:post_tag_section, post: post_record, tag:,
                                 begin_ms: 1000, end_ms: 2000)
 
-      tn2 = TagName.create!(name: 'spec_tag_2')
-      replacement_tag = Tag.create!(tag_name: tn2, category: :general)
+      tn2 = create(:tag_name, name: 'spec_tag_2')
+      replacement_tag = create(:tag, primary_tag_name: tn2, category: :general)
 
       put "/posts/#{post_record.id}", params: post_update_params(
           post_record,
@@ -1707,11 +1717,10 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     it 'rejects a deprecated tag specified directly' do
-      Tag.create!(
-        name: 'deprecated_update_tag',
-        category: :general,
-        deprecated_at: Time.current
-      )
+      create(:tag,
+          primary_name: 'deprecated_update_tag',
+          category: :general,
+          deprecated_at: Time.current)
       sign_in_as(member)
 
       put "/posts/#{ post_record.id }", params: post_update_params(
@@ -1966,7 +1975,7 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: 'updated by me',
-            tags: "spec_tag #{Tag.no_deerjikist.name}")
+            tags: "spec_tag #{primary_tag_name_for(Tag.no_deerjikist, 'ja').name}")
 
         expect(response).to have_http_status(:conflict)
 
@@ -1986,7 +1995,8 @@ RSpec.describe 'Posts API', type: :request do
 
         base_version = create_post_version_for!(post_record.reload)
 
-        current_tag = Tag.find_or_create_by_tag_name!('current_added_tag', category: :general)
+        current_tag = Tag.find_or_create_by_tag_name!(
+            Locale.nipponese, 'current_added_tag', category: :general)
         PostTag.create!(post: post_record, tag: current_tag, created_user: member)
 
         PostVersionRecorder.record!(
@@ -1997,7 +2007,8 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: "spec_tag #{Tag.no_deerjikist.name} incoming_added_tag")
+            tags: ['spec_tag', primary_tag_name_for(Tag.no_deerjikist, 'ja').name,
+                   'incoming_added_tag'].join(' '))
 
         expect(response).to have_http_status(:conflict)
 
@@ -2015,7 +2026,8 @@ RSpec.describe 'Posts API', type: :request do
 
         base_version = create_post_version_for!(post_record.reload)
 
-        current_tag = Tag.find_or_create_by_tag_name!('current_merge_tag', category: :general)
+        current_tag = Tag.find_or_create_by_tag_name!(
+            Locale.nipponese, 'current_merge_tag', category: :general)
         PostTag.create!(post: post_record, tag: current_tag, created_user: member)
 
         PostVersionRecorder.record!(
@@ -2026,15 +2038,17 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: "spec_tag #{Tag.no_deerjikist.name} incoming_merge_tag",
+            tags: ['spec_tag', primary_tag_name_for(Tag.no_deerjikist, 'ja').name,
+                   'incoming_merge_tag'].join(' '),
             merge: '1')
 
         expect(response).to have_http_status(:ok)
 
-        names = post_record.reload.tags.map(&:name)
+        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
+                              language_code: 'ja', primary_flg: true).pluck(:name)
 
         expect(names).to include('spec_tag')
-        expect(names).to include(Tag.no_deerjikist.name)
+        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
         expect(names).to include('current_merge_tag')
         expect(names).to include('incoming_merge_tag')
       end
@@ -2057,14 +2071,15 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: "spec_tag #{ Tag.no_deerjikist.name }")
+            tags: "spec_tag #{ primary_tag_name_for(Tag.no_deerjikist, 'ja').name }")
 
         expect(response).to have_http_status(:ok)
 
-        names = post_record.reload.tags.map(&:name)
+        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
+                              language_code: 'ja', primary_flg: true).pluck(:name)
 
         expect(names).to include('spec_tag')
-        expect(names).to include(Tag.no_deerjikist.name)
+        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
         expect(post_record.external_tags).to contain_exactly(nico_tag)
       end
 
@@ -2079,14 +2094,15 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: 'updated title',
-            tags: "spec_tag #{ Tag.no_deerjikist.name }")
+            tags: "spec_tag #{ primary_tag_name_for(Tag.no_deerjikist, 'ja').name }")
 
         expect(response).to have_http_status(:ok)
 
-        names = post_record.reload.tags.map(&:name)
+        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
+                              language_code: 'ja', primary_flg: true).pluck(:name)
 
         expect(names).to include('spec_tag')
-        expect(names).to include(Tag.no_deerjikist.name)
+        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
         expect(post_record.external_tags).to contain_exactly(nico_tag)
 
         external_json =
@@ -2102,7 +2118,8 @@ RSpec.describe 'Posts API', type: :request do
         sign_in_as(member)
 
         nico_tag = create_nico_tag!('nico:relation_source')
-        linked_tag = Tag.find_or_create_by_tag_name!('relation_linked_tag', category: :general)
+        linked_tag = Tag.find_or_create_by_tag_name!(
+            Locale.nipponese, 'relation_linked_tag', category: :general)
 
         NicoTagRelation.create!(nico_tag:, tag: linked_tag)
         PostExternalTag.create!(post: post_record, external_tag: nico_tag)
@@ -2113,16 +2130,17 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: "spec_tag #{ Tag.no_deerjikist.name }")
+            tags: "spec_tag #{ primary_tag_name_for(Tag.no_deerjikist, 'ja').name }")
 
         expect(response).to have_http_status(:ok)
 
-        names = post_record.reload.tags.map(&:name)
+        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
+                              language_code: 'ja', primary_flg: true).pluck(:name)
 
         expect(post_record.external_tags).to contain_exactly(nico_tag)
         expect(names).to include('spec_tag')
-        expect(names).to include(Tag.no_deerjikist.name)
-        expect(names).not_to include(linked_tag.name)
+        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
+        expect(names).not_to include(primary_tag_name_for(linked_tag, 'ja').name)
       end
 
       it 'force-updates stale posts without base_version_no' do
@@ -2138,7 +2156,7 @@ RSpec.describe 'Posts API', type: :request do
 
         put "/posts/#{post_record.id}", params: post_write_params(
             title: 'forced title',
-            tags: "spec_tag #{Tag.no_deerjikist.name}",
+            tags: "spec_tag #{primary_tag_name_for(Tag.no_deerjikist, 'ja').name}",
             force: '1')
 
         expect(response).to have_http_status(:ok)
@@ -2191,8 +2209,8 @@ RSpec.describe 'Posts API', type: :request do
     let(:oc_from) { Time.zone.local(2019, 12, 31, 0, 0, 0) }
     let(:oc_before) { Time.zone.local(2020, 1, 1, 0, 0, 0) }
 
-    let!(:tag_name2) { TagName.create!(name: 'spec_tag_2') }
-    let!(:tag2) { Tag.create!(tag_name: tag_name2, category: :general) }
+    let!(:tag_name2) { create(:tag_name, name: 'spec_tag_2') }
+    let!(:tag2) { create(:tag, primary_tag_name: tag_name2, category: :general) }
 
     def snapshot_tags(post)
       post.snapshot_tag_names.join(' ')
@@ -2417,7 +2435,7 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:ok)
       expect(json.fetch('count')).to eq(3)
       expect(json.fetch('versions').first.fetch('tags')).to include(
-          'name' => tag2.name, 'type' => 'context')
+          'name' => primary_tag_name_for(tag2, 'ja').name, 'type' => 'context')
     end
 
     it 'filters versions by tag when the current snapshot includes the tag' do
@@ -2550,8 +2568,8 @@ RSpec.describe 'Posts API', type: :request do
       sign_in_as(member)
       base_version = create_post_version_for!(post_record)
 
-      tag_name2 = TagName.create!(name: 'spec_tag_2')
-      Tag.create!(tag_name: tag_name2, category: :general)
+      tag_name2 = create(:tag_name, name: 'spec_tag_2')
+      create(:tag, primary_tag_name: tag_name2, category: :general)
 
       expect do
         put "/posts/#{post_record.id}", params: post_write_params(
@@ -2715,8 +2733,8 @@ RSpec.describe 'Posts API', type: :request do
 
       base_version = create_post_version_for!(post_record.reload)
 
-      tag_name2 = TagName.create!(name: 'spec_tag_2')
-      tag2 = Tag.create!(tag_name: tag_name2, category: :general)
+      tag_name2 = create(:tag_name, name: 'spec_tag_2')
+      tag2 = create(:tag, primary_tag_name: tag_name2, category: :general)
 
       expect {
         put "/posts/#{post_record.id}", params: post_write_params(
diff --git a/backend/spec/requests/tag_versions_spec.rb b/backend/spec/requests/tag_versions_spec.rb
index 62afeb8..f105773 100644
--- a/backend/spec/requests/tag_versions_spec.rb
+++ b/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!(
diff --git a/backend/spec/requests/tag_wiki_history_integrity_spec.rb b/backend/spec/requests/tag_wiki_history_integrity_spec.rb
index 4914cf4..a464c05 100644
--- a/backend/spec/requests/tag_wiki_history_integrity_spec.rb
+++ b/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
diff --git a/backend/spec/requests/tags_deerjikists_spec.rb b/backend/spec/requests/tags_deerjikists_spec.rb
index e0d3a3e..e0c2314 100644
--- a/backend/spec/requests/tags_deerjikists_spec.rb
+++ b/backend/spec/requests/tags_deerjikists_spec.rb
@@ -12,7 +12,7 @@ RSpec.describe 'Tags deerjikists API', type: :request do
   let(:guest) { create(:user, role: :guest) }
 
   before do
-    tag.tag_name.update!(name: 'deerjika')
+    primary_tag_name_for(tag, 'ja').update!(name: 'deerjika')
   end
 
   describe 'GET /tags/:id/deerjikists' do
@@ -344,7 +344,7 @@ RSpec.describe 'Tags deerjikists API', type: :request do
         end
 
         before do
-          other_tag.tag_name.update!(name: 'existing-deerjikist')
+          primary_tag_name_for(other_tag, 'ja').update!(name: 'existing-deerjikist')
         end
 
         it 'returns an indexed 422 error and rolls back the complete replacement' do
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index 3c1088c..c8bfd54 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -2,13 +2,13 @@ require 'cgi'
 require 'rails_helper'
 
 RSpec.describe 'Tags API', type: :request do
-  let!(:tn) { TagName.create!(name: 'spec_tag') }
-  let!(:tag) { Tag.create!(tag_name: tn, category: :general) }
-  let!(:alias_tn) { TagName.create!(name: 'unko', canonical: tn) }
+  let!(:tn) { create(:tag_name, name: 'spec_tag') }
+  let!(:tag) { create(:tag, primary_tag_name: tn, category: :general) }
+  let!(:alias_tn) { create(:tag_name, :alias, name: 'unko', tag:) }
   let!(:post) { Post.create!(url: 'https://example.com/unkounkounko') }
   let!(:post_tag) { PostTag.create!(post:, tag:) }
-  let!(:tn2) { TagName.create!(name: 'unknown') }
-  let!(:tag2) { Tag.create!(tag_name: tn2, category: :general) }
+  let!(:tn2) { create(:tag_name, name: 'unknown') }
+  let!(:tag2) { create(:tag, primary_tag_name: tn2, category: :general) }
 
   def response_tags
     json.fetch('tags')
@@ -18,6 +18,14 @@ RSpec.describe 'Tags API', type: :request do
     response_tags.map { |t| t.fetch('name') }
   end
 
+  def version_primary_name(version, language_code)
+    version.names.fetch(language_code).fetch('name')
+  end
+
+  def version_alias_names(version, language_code)
+    version.names.fetch(language_code).fetch('aliases').pluck('name')
+  end
+
   def dummy_material_upload(filename: 'dummy.png', type: 'image/png', body: 'dummy')
     Rack::Test::UploadedFile.new(StringIO.new(body), type, original_filename: filename)
   end
@@ -38,7 +46,9 @@ RSpec.describe 'Tags API', type: :request do
       expect(response).to have_http_status(:ok)
       expect(json.fetch('count')).to eq(2)
       expect(response_tags).to contain_exactly(
-          a_hash_including('id' => tag.id, 'name' => tag.name, 'category' => 'general'),
+          a_hash_including('id' => tag.id,
+                           'name' => primary_tag_name_for(tag, 'ja').name,
+                           'category' => 'general'),
           a_hash_including(
               'id' => external.id,
               'name' => 'nico:spec_external',
@@ -91,7 +101,7 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'filters tags by category' do
-      meme = Tag.create!(tag_name: TagName.create!(name: 'meme_only'), category: :meme)
+      meme = create(:tag, primary_name: 'meme_only', category: :meme)
 
       get '/tags', params: { category: 'meme' }
 
@@ -101,30 +111,29 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'filters tags by deprecated state' do
-      deprecated_tag = Tag.create!(
-        name: 'deprecated_filter',
-        category: :general,
-        deprecated_at: 1.day.from_now
-      )
-      active_tag = Tag.create!(name: 'active_filter', category: :general)
+      deprecated_tag = create(:tag,
+          primary_name: 'deprecated_filter',
+          category: :general,
+          deprecated_at: 1.day.from_now)
+      active_tag = create(:tag, primary_name: 'active_filter', category: :general)
 
       get '/tags', params: { name: '_filter', deprecated: '1' }
 
       expect(response).to have_http_status(:ok)
-      expect(response_names).to include(deprecated_tag.name)
-      expect(response_names).not_to include(active_tag.name)
+      expect(response_names).to include(primary_tag_name_for(deprecated_tag, 'ja').name)
+      expect(response_names).not_to include(primary_tag_name_for(active_tag, 'ja').name)
 
       get '/tags', params: { name: '_filter', deprecated: '0' }
 
       expect(response).to have_http_status(:ok)
-      expect(response_names).to include(active_tag.name)
-      expect(response_names).not_to include(deprecated_tag.name)
+      expect(response_names).to include(primary_tag_name_for(active_tag, 'ja').name)
+      expect(response_names).not_to include(primary_tag_name_for(deprecated_tag, 'ja').name)
     end
 
     it 'filters tags by post_count range' do
-      low = Tag.create!(tag_name: TagName.create!(name: 'pc_low'), category: :general)
-      mid = Tag.create!(tag_name: TagName.create!(name: 'pc_mid'), category: :general)
-      high = Tag.create!(tag_name: TagName.create!(name: 'pc_high'), category: :general)
+      low = create(:tag, primary_name: 'pc_low', category: :general)
+      mid = create(:tag, primary_name: 'pc_mid', category: :general)
+      high = create(:tag, primary_name: 'pc_high', category: :general)
 
       low.update_columns(post_count: 1)
       mid.update_columns(post_count: 3)
@@ -142,8 +151,8 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'filters tags by created_at range' do
-      old_tag = Tag.create!(tag_name: TagName.create!(name: 'created_old'), category: :general)
-      new_tag = Tag.create!(tag_name: TagName.create!(name: 'created_new'), category: :general)
+      old_tag = create(:tag, primary_name: 'created_old', category: :general)
+      new_tag = create(:tag, primary_name: 'created_new', category: :general)
 
       old_time = Time.zone.local(2024, 1, 1, 0, 0, 0)
       new_time = Time.zone.local(2024, 2, 1, 0, 0, 0)
@@ -162,8 +171,8 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'filters tags by updated_at range' do
-      old_tag = Tag.create!(tag_name: TagName.create!(name: 'updated_old'), category: :general)
-      new_tag = Tag.create!(tag_name: TagName.create!(name: 'updated_new'), category: :general)
+      old_tag = create(:tag, primary_name: 'updated_old', category: :general)
+      new_tag = create(:tag, primary_name: 'updated_new', category: :general)
 
       old_time = Time.zone.local(2024, 3, 1, 0, 0, 0)
       new_time = Time.zone.local(2024, 4, 1, 0, 0, 0)
@@ -182,12 +191,12 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'orders tags by custom category order' do
-      Tag.create!(tag_name: TagName.create!(name: 'cat_deerjikist'), category: :deerjikist)
-      Tag.create!(tag_name: TagName.create!(name: 'cat_meme'), category: :meme)
-      Tag.create!(tag_name: TagName.create!(name: 'cat_character'), category: :character)
-      Tag.create!(tag_name: TagName.create!(name: 'cat_general'), category: :general)
-      Tag.create!(tag_name: TagName.create!(name: 'cat_material'), category: :material)
-      Tag.create!(tag_name: TagName.create!(name: 'cat_meta'), category: :meta)
+      create(:tag, primary_name: 'cat_deerjikist', category: :deerjikist)
+      create(:tag, primary_name: 'cat_meme', category: :meme)
+      create(:tag, primary_name: 'cat_character', category: :character)
+      create(:tag, primary_name: 'cat_general', category: :general)
+      create(:tag, primary_name: 'cat_material', category: :material)
+      create(:tag, primary_name: 'cat_meta', category: :meta)
       create(:external_tag, name: 'cat_nico')
 
       get '/tags', params: { name: 'cat_', order: 'category:asc', limit: 20 }
@@ -202,20 +211,20 @@ RSpec.describe 'Tags API', type: :request do
     context 'with mixed legacy pagination' do
       let!(:first_tag) do
         create(:tag,
-               tag_name: create(:tag_name, name: 'a_mixed_page'),
-               category: :meme)
+            primary_tag_name: create(:tag_name, name: 'a_mixed_page'),
+            category: :meme)
       end
 
       let!(:middle_tag) do
         create(:tag,
-               tag_name: create(:tag_name, name: 'm_mixed_page'),
-               category: :meta)
+            primary_tag_name: create(:tag_name, name: 'm_mixed_page'),
+            category: :meta)
       end
 
       let!(:last_tag) do
         create(:tag,
-               tag_name: create(:tag_name, name: 'z_mixed_page'),
-               category: :general)
+            primary_tag_name: create(:tag_name, name: 'z_mixed_page'),
+            category: :general)
       end
 
       let!(:first_external) do
@@ -265,7 +274,7 @@ RSpec.describe 'Tags API', type: :request do
 
     it 'paginates and keeps total count' do
       %w[pag_a pag_b pag_c].each do |name|
-        Tag.create!(tag_name: TagName.create!(name:), category: :general)
+        create(:tag, primary_tag_name: create(:tag_name, name:), category: :general)
       end
 
       get '/tags', params: { name: 'pag_', order: 'name:asc', page: 2, limit: 2 }
@@ -276,8 +285,8 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'falls back to default ordering when order is invalid' do
-      low = Tag.create!(tag_name: TagName.create!(name: 'fallback_low'), category: :general)
-      high = Tag.create!(tag_name: TagName.create!(name: 'fallback_high'), category: :general)
+      low = create(:tag, primary_name: 'fallback_low', category: :general)
+      high = create(:tag, primary_name: 'fallback_high', category: :general)
 
       low.update_columns(post_count: 1)
       high.update_columns(post_count: 9)
@@ -290,7 +299,7 @@ RSpec.describe 'Tags API', type: :request do
 
     it 'normalises invalid page and limit' do
       %w[norm_a norm_b].each do |name|
-        Tag.create!(tag_name: TagName.create!(name:), category: :general)
+        create(:tag, primary_tag_name: create(:tag_name, name:), category: :general)
       end
 
       get '/tags', params: { name: 'norm_', order: 'name:asc', page: 0, limit: 0 }
@@ -302,10 +311,9 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'returns aliases and parent tags' do
-      parent_tag = Tag.create!(
-        tag_name: TagName.create!(name: 'index_parent_tag'),
-        category: :meme
-      )
+      parent_tag = create(:tag,
+          primary_tag_name: create(:tag_name, name: 'index_parent_tag'),
+          category: :meme)
       TagImplication.create!(tag:, parent_tag:)
 
       get '/tags', params: { name: 'spec_tag' }
@@ -349,10 +357,9 @@ RSpec.describe 'Tags API', type: :request do
       end
 
       it 'returns aliases and parent tags' do
-        parent_tag = Tag.create!(
-          tag_name: TagName.create!(name: 'show_parent_tag'),
-          category: :character
-        )
+        parent_tag = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'show_parent_tag'),
+            category: :character)
         TagImplication.create!(tag:, parent_tag:)
 
         request
@@ -398,7 +405,7 @@ RSpec.describe 'Tags API', type: :request do
     it 'prefers Tag when Tag and ExternalTag have the same id' do
       internal = create(
           :tag,
-          tag_name: create(:tag_name, name: 'internal_collision'))
+          primary_tag_name: create(:tag_name, name: 'internal_collision'))
       create(
           :external_tag,
           id: internal.id,
@@ -416,7 +423,7 @@ RSpec.describe 'Tags API', type: :request do
 
   describe 'GET /tags/autocomplete' do
     it 'combines internal and external matches without conflating equal ids' do
-      internal = Tag.create!(category: :general, name: 'mixed_internal', post_count: 2)
+      internal = create(:tag, category: :general, primary_name: 'mixed_internal', post_count: 2)
       external = create(:external_tag, id: internal.id,
                                        name: 'mixed_external', post_count: 3)
 
@@ -455,7 +462,7 @@ RSpec.describe 'Tags API', type: :request do
     it 'limits the combined results to 20 and sorts ties by displayed name' do
       11.times do |i|
         name = "combined_#{ i.to_s.rjust(2, '0') }"
-        Tag.create!(category: :general, name:, post_count: 1)
+        create(:tag, category: :general, primary_name: name, post_count: 1)
         create(:external_tag, name:, post_count: 1)
       end
 
@@ -467,34 +474,39 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'excludes external tags but preserves internal alias matches when nico is false' do
-      internal = Tag.create!(category: :general, name: 'switch_internal', post_count: 1)
-      alias_target = Tag.create!(category: :general, name: 'alias_target', post_count: 1)
-      TagName.create!(name: 'switch_alias', canonical: alias_target.tag_name)
+      internal = create(:tag, category: :general, primary_name: 'switch_internal', post_count: 1)
+      alias_target = create(:tag, category: :general, primary_name: 'alias_target', post_count: 1)
+      create(:tag_name, :alias, name: 'switch_alias', tag: alias_target)
       create(:external_tag, name: 'switch_external', post_count: 1)
 
       get '/tags/autocomplete', params: { q: 'switch', nico: '0' }
 
       expect(response).to have_http_status(:ok)
       expect(json).to contain_exactly(
-          a_hash_including('id' => internal.id, 'name' => internal.name),
-          a_hash_including('id' => alias_target.id, 'name' => alias_target.name,
+          a_hash_including('id' => internal.id,
+                           'name' => primary_tag_name_for(internal, 'ja').name),
+          a_hash_including('id' => alias_target.id,
+                           'name' => primary_tag_name_for(alias_target, 'ja').name,
                            'matched_alias' => 'switch_alias'))
     end
 
     ['%', '_'].each do |wildcard|
-      it "treats #{ wildcard } literally for canonical, alias, and external names" do
+      it "treats #{ wildcard } literally for primary, alias, and external names" do
         literal = "literal#{ wildcard }match"
-        Tag.create!(category: :general, name: literal, post_count: 1)
-        alias_target = Tag.create!(category: :general, name: 'literal_alias_target', post_count: 1)
-        TagName.create!(name: "#{ literal }_alias", canonical: alias_target.tag_name)
+        create(:tag, category: :general, primary_name: literal, post_count: 1)
+        alias_target = create(
+            :tag, category: :general, primary_name: 'literal_alias_target', post_count: 1)
+        create(:tag_name, :alias, name: "#{ literal }_alias",
+                                  tag: alias_target)
         create(:external_tag, name: literal, post_count: 1)
-        Tag.create!(category: :general, name: 'literalXmatch', post_count: 2)
+        create(:tag, category: :general, primary_name: 'literalXmatch', post_count: 2)
         create(:external_tag, name: 'literalXmatch', post_count: 2)
 
         get '/tags/autocomplete', params: { q: "literal#{ wildcard }" }
 
         expect(json.map { |row| row.fetch('name') })
-            .to contain_exactly(literal, alias_target.name, "nico:#{ literal }")
+            .to contain_exactly(
+                literal, primary_tag_name_for(alias_target, 'ja').name, "nico:#{ literal }")
       end
     end
 
@@ -510,7 +522,7 @@ RSpec.describe 'Tags API', type: :request do
       expect(t['matched_alias']).to be(nil)
     end
 
-    it 'returns matching canonical tags by q with aliases' do
+    it 'returns matching primary tag names by q with aliases' do
       get '/tags/autocomplete', params: { q: 'unk' }
 
       expect(response).to have_http_status(:ok)
@@ -523,11 +535,10 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'omits deprecated tags' do
-      deprecated_tag = Tag.create!(
-        name: 'spec_deprecated',
-        category: :general,
-        deprecated_at: Time.current
-      )
+      deprecated_tag = create(:tag,
+          primary_name: 'spec_deprecated',
+          category: :general,
+          deprecated_at: Time.current)
       deprecated_tag.update_columns(post_count: 1)
 
       get '/tags/autocomplete', params: { q: 'spec_', present: '0' }
@@ -621,7 +632,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(response).to have_http_status(:ok)
 
         tag.reload
-        expect(tag.name).to eq('new')
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('new')
         expect(tag.category).to eq('general')
 
         body = JSON.parse(response.body)
@@ -636,7 +647,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(response).to have_http_status(:ok)
 
         tag.reload
-        expect(tag.name).to eq('spec_tag')
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('spec_tag')
         expect(tag.category).to eq('meme')
       end
 
@@ -646,7 +657,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(response).to have_http_status(:ok)
 
         tag.reload
-        expect(tag.name).to eq('spec_tag')
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('spec_tag')
         expect(tag.category).to eq('general')
       end
 
@@ -656,7 +667,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(response).to have_http_status(:ok)
 
         tag.reload
-        expect(tag.name).to eq('n')
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('n')
         expect(tag.category).to eq('meta')
       end
 
@@ -669,7 +680,7 @@ RSpec.describe 'Tags API', type: :request do
         patch "/tags/#{tag.id}", params: { name: 'new', category: 'nico' }
 
         expect(response).to have_http_status(:unprocessable_entity)
-        expect(tag.reload.name).to eq('spec_tag')
+        expect(primary_tag_name_for(tag.reload, 'ja').name).to eq('spec_tag')
         expect(tag.category).to eq('general')
       end
 
@@ -684,11 +695,11 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(versions.map(&:event_type)).to eq(['create', 'update'])
 
-        expect(versions.first.name).to eq('spec_tag')
+        expect(version_primary_name(versions.first, 'ja')).to eq('spec_tag')
         expect(versions.first.category).to eq('general')
-        expect(versions.first.aliases.split).to include('unko')
+        expect(version_alias_names(versions.first, 'ja')).to include('unko')
 
-        expect(versions.second.name).to eq('new_tag_name')
+        expect(version_primary_name(versions.second, 'ja')).to eq('new_tag_name')
         expect(versions.second.category).to eq('meme')
         expect(versions.second.created_by_user_id).to eq(member_user.id)
       end
@@ -719,7 +730,7 @@ RSpec.describe 'Tags API', type: :request do
       it 'PATCH で tag の name を変更すると対応する wiki version を作成する' do
         wiki_page =
             Wiki::Commit.create_content!(
-                tag_name: tag.tag_name,
+                tag_name: primary_tag_name_for(tag, 'ja'),
                 body: 'wiki body before',
                 created_by_user: member_user,
                 message: 'init')
@@ -747,7 +758,7 @@ RSpec.describe 'Tags API', type: :request do
       it 'tag の category だけを変更しても wiki version は作成しない' do
         wiki_page =
             Wiki::Commit.create_content!(
-                tag_name: tag.tag_name,
+                tag_name: primary_tag_name_for(tag, 'ja'),
                 body: 'wiki body before',
                 created_by_user: member_user,
                 message: 'init')
@@ -774,7 +785,8 @@ RSpec.describe 'Tags API', type: :request do
         }
 
         expect(response).to have_http_status(:ok)
-        expect(TagName.find_by!(name: 'spec_tag').canonical).to eq(tag.reload.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'spec_tag'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
 
         patch "/tags/#{ tag.id }", params: { name: 'spec_tag' }
 
@@ -782,15 +794,17 @@ RSpec.describe 'Tags API', type: :request do
 
         tag.reload
 
-        expect(tag.name).to eq('spec_tag')
-        expect(tag.tag_name.canonical_id).to be_nil
-        expect(TagName.find_by!(name: 'patch_roundtrip_target').canonical).to eq(tag.tag_name)
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('spec_tag')
+        expect(primary_tag_name_for(tag, 'ja')).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: true)
+        expect(TagName.find_by!(language_code: 'ja', name: 'patch_roundtrip_target'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
       end
 
       it '別 tag の正規名には変更できない' do
         wiki_page =
             Wiki::Commit.create_content!(
-                tag_name: tag.tag_name,
+                tag_name: primary_tag_name_for(tag, 'ja'),
                 body: 'patch collision wiki',
                 created_by_user: member_user,
                 message: 'init')
@@ -802,9 +816,10 @@ RSpec.describe 'Tags API', type: :request do
           'name' => ['その名前は既に使はれてゐます．']
         )
 
-        expect(tag.reload.name).to eq('spec_tag')
-        expect(tag.tag_name.aliases.map(&:name)).to contain_exactly('unko')
-        expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
+        expect(primary_tag_name_for(tag.reload, 'ja').name).to eq('spec_tag')
+        expect(TagName.where(tag_id: tag.id, language_code: 'ja', primary_flg: false).pluck(:name))
+            .to contain_exactly('unko')
+        expect(wiki_page.reload.tag_name).to eq(primary_tag_name_for(tag, 'ja'))
       end
 
       it 'system tag の name は変更できない' do
@@ -813,34 +828,34 @@ RSpec.describe 'Tags API', type: :request do
         patch "/tags/#{ system_tag.id }", params: { name: 'patch_system_tag_renamed' }
 
         expect(response).to have_http_status(:unprocessable_entity)
-        expect(system_tag.reload.name).to eq('bot操作')
+        expect(primary_tag_name_for(system_tag.reload, 'ja').name).to eq('bot操作')
       end
     end
   end
 
   describe 'GET /tags/with-depth' do
     let!(:root_meme) do
-      Tag.create!(tag_name: TagName.create!(name: 'depth_a_root_meme'), category: :meme)
+      create(:tag, primary_name: 'depth_a_root_meme', category: :meme)
     end
 
     let!(:root_material) do
-      Tag.create!(tag_name: TagName.create!(name: 'depth_b_root_material'), category: :material)
+      create(:tag, primary_name: 'depth_b_root_material', category: :material)
     end
 
     let!(:hidden_general_root) do
-      Tag.create!(tag_name: TagName.create!(name: 'depth_hidden_general_root'), category: :general)
+      create(:tag, primary_name: 'depth_hidden_general_root', category: :general)
     end
 
     let!(:child_character) do
-      Tag.create!(tag_name: TagName.create!(name: 'depth_child_character'), category: :character)
+      create(:tag, primary_name: 'depth_child_character', category: :character)
     end
 
     let!(:grandchild_material) do
-      Tag.create!(tag_name: TagName.create!(name: 'depth_grandchild_material'), category: :material)
+      create(:tag, primary_name: 'depth_grandchild_material', category: :material)
     end
 
     let!(:child_general) do
-      Tag.create!(tag_name: TagName.create!(name: 'depth_child_general'), category: :general)
+      create(:tag, primary_name: 'depth_child_general', category: :general)
     end
 
     before do
@@ -883,15 +898,13 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'passes through deprecated tags when finding children' do
-      deprecated_middle = Tag.create!(
-        name: 'depth_deprecated_middle',
-        category: :character,
-        deprecated_at: Time.current
-      )
-      visible_descendant = Tag.create!(
-        name: 'depth_visible_descendant',
-        category: :material
-      )
+      deprecated_middle = create(:tag,
+          primary_name: 'depth_deprecated_middle',
+          category: :character,
+          deprecated_at: Time.current)
+      visible_descendant = create(:tag,
+          primary_name: 'depth_visible_descendant',
+          category: :material)
       TagImplication.create!(parent_tag: root_material, tag: deprecated_middle)
       TagImplication.create!(parent_tag: deprecated_middle, tag: visible_descendant)
 
@@ -903,24 +916,20 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'passes through multiple deprecated tags for roots and has_children' do
-      active_child = Tag.create!(
-        name: 'depth_active_child_below_deprecated',
-        category: :character
-      )
-      deprecated_parent = Tag.create!(
-        name: 'depth_deprecated_parent',
-        category: :character,
-        deprecated_at: Time.current
-      )
-      deprecated_grandparent = Tag.create!(
-        name: 'depth_deprecated_grandparent',
-        category: :material,
-        deprecated_at: Time.current
-      )
-      active_ancestor = Tag.create!(
-        name: 'depth_active_ancestor',
-        category: :meme
-      )
+      active_child = create(:tag,
+          primary_name: 'depth_active_child_below_deprecated',
+          category: :character)
+      deprecated_parent = create(:tag,
+          primary_name: 'depth_deprecated_parent',
+          category: :character,
+          deprecated_at: Time.current)
+      deprecated_grandparent = create(:tag,
+          primary_name: 'depth_deprecated_grandparent',
+          category: :material,
+          deprecated_at: Time.current)
+      active_ancestor = create(:tag,
+          primary_name: 'depth_active_ancestor',
+          category: :meme)
       TagImplication.create!(tag: active_child, parent_tag: deprecated_parent)
       TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
       TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_ancestor)
@@ -945,15 +954,13 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'treats an active tag with only deprecated ancestors as a root' do
-      active_child = Tag.create!(
-        name: 'depth_root_below_deprecated',
-        category: :character
-      )
-      deprecated_parent = Tag.create!(
-        name: 'depth_root_deprecated_parent',
-        category: :material,
-        deprecated_at: Time.current
-      )
+      active_child = create(:tag,
+          primary_name: 'depth_root_below_deprecated',
+          category: :character)
+      deprecated_parent = create(:tag,
+          primary_name: 'depth_root_deprecated_parent',
+          category: :material,
+          deprecated_at: Time.current)
       TagImplication.create!(tag: active_child, parent_tag: deprecated_parent)
 
       get '/tags/with-depth'
@@ -967,16 +974,14 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'terminates when deprecated implications contain a cycle' do
-      first = Tag.create!(
-        name: 'depth_cycle_first',
-        category: :character,
-        deprecated_at: Time.current
-      )
-      second = Tag.create!(
-        name: 'depth_cycle_second',
-        category: :material,
-        deprecated_at: Time.current
-      )
+      first = create(:tag,
+          primary_name: 'depth_cycle_first',
+          category: :character,
+          deprecated_at: Time.current)
+      second = create(:tag,
+          primary_name: 'depth_cycle_second',
+          category: :material,
+          deprecated_at: Time.current)
       TagImplication.create!(tag: first, parent_tag: root_material)
       TagImplication.create!(tag: second, parent_tag: first)
       now = Time.current
@@ -1002,19 +1007,19 @@ RSpec.describe 'Tags API', type: :request do
     let!(:material_user) { create_member_user! }
 
     let!(:root_tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'materials_root'), category: :material)
+      create(:tag, primary_name: 'materials_root', category: :material)
     end
 
     let!(:child_a_tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'materials_child_a'), category: :material)
+      create(:tag, primary_name: 'materials_child_a', category: :material)
     end
 
     let!(:child_b_tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'materials_child_b'), category: :character)
+      create(:tag, primary_name: 'materials_child_b', category: :character)
     end
 
     let!(:grandchild_tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'materials_grandchild'), category: :material)
+      create(:tag, primary_name: 'materials_grandchild', category: :material)
     end
 
     let!(:root_material) do
@@ -1036,7 +1041,7 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     it 'returns a tag tree with nested materials sorted by child name' do
-      get "/tags/name/#{ CGI.escape(root_tag.name) }/materials"
+      get "/tags/name/#{ CGI.escape(primary_tag_name_for(root_tag, 'ja').name) }/materials"
 
       expect(response).to have_http_status(:ok)
 
@@ -1127,7 +1132,7 @@ RSpec.describe 'Tags API', type: :request do
         }
 
         expect(response).to have_http_status(:unprocessable_entity)
-        expect(tag.reload.name).to eq('spec_tag')
+        expect(primary_tag_name_for(tag.reload, 'ja').name).to eq('spec_tag')
       end
 
       it 'category が空なら 422 を返す' do
@@ -1139,7 +1144,7 @@ RSpec.describe 'Tags API', type: :request do
         }
 
         expect(response).to have_http_status(:unprocessable_entity)
-        expect(tag.reload.name).to eq('spec_tag')
+        expect(primary_tag_name_for(tag.reload, 'ja').name).to eq('spec_tag')
         expect(tag.category).to eq('general')
       end
 
@@ -1158,14 +1163,12 @@ RSpec.describe 'Tags API', type: :request do
       end
 
       it 'name, category, aliases, parent tags をまとめて更新できる' do
-        old_parent = Tag.create!(
-          tag_name: TagName.create!(name: 'put_old_parent'),
-          category: :general
-        )
-        kept_parent = Tag.create!(
-          tag_name: TagName.create!(name: 'put_kept_parent'),
-          category: :general
-        )
+        old_parent = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'put_old_parent'),
+            category: :general)
+        kept_parent = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'put_kept_parent'),
+            category: :general)
         TagImplication.create!(tag:, parent_tag: old_parent)
         TagImplication.create!(tag:, parent_tag: kept_parent)
 
@@ -1181,22 +1184,24 @@ RSpec.describe 'Tags API', type: :request do
 
         tag.reload
 
-        expect(tag.name).to eq('put_renamed_tag')
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('put_renamed_tag')
         expect(tag.category).to eq('meme')
 
-        expect(TagName.find_by(name: 'put_alias_a').canonical).to eq(tag.tag_name)
-        expect(TagName.find_by(name: 'put_alias_b').canonical).to eq(tag.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_alias_a'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_alias_b'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
 
-        old_name_alias = TagName.find_by(name: 'spec_tag')
+        old_name_alias = TagName.find_by(language_code: 'ja', name: 'spec_tag')
         expect(old_name_alias).to be_present
-        expect(old_name_alias.canonical).to eq(tag.tag_name)
+        expect(old_name_alias).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: false)
 
-        expect(alias_tn.reload.canonical).to be_nil
+        expect(alias_tn.reload.tag_id).to be_nil
 
-        expect(tag.parents.map(&:name)).to contain_exactly(
-          'put_kept_parent',
-          'put_new_parent'
-        )
+        expect(TagName.where(tag_id: tag.parents.select(:id),
+                             language_code: 'ja', primary_flg: true).pluck(:name))
+            .to contain_exactly('put_kept_parent', 'put_new_parent')
 
         expect(TagImplication.where(tag:, parent_tag: old_parent)).not_to exist
 
@@ -1226,7 +1231,8 @@ RSpec.describe 'Tags API', type: :request do
 
         tag.reload
 
-        expect(TagName.find_by(name: 'put_alias_self_test').canonical).to eq(tag.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_alias_self_test'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
         expect(json['aliases']).to include('put_alias_self_test')
         expect(json['aliases']).not_to include('spec_tag')
       end
@@ -1263,13 +1269,13 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(versions.map(&:event_type)).to eq(['create', 'update'])
 
-        expect(versions.first.name).to eq('spec_tag')
+        expect(version_primary_name(versions.first, 'ja')).to eq('spec_tag')
         expect(versions.first.category).to eq('general')
-        expect(versions.first.aliases.split).to include('unko')
+        expect(version_alias_names(versions.first, 'ja')).to include('unko')
 
-        expect(versions.second.name).to eq('put_versioned_tag')
+        expect(version_primary_name(versions.second, 'ja')).to eq('put_versioned_tag')
         expect(versions.second.category).to eq('meta')
-        expect(versions.second.aliases.split).to include('spec_tag')
+        expect(version_alias_names(versions.second, 'ja')).to include('spec_tag')
         expect(versions.second.created_by_user_id).to eq(member_user.id)
       end
 
@@ -1296,35 +1302,37 @@ RSpec.describe 'Tags API', type: :request do
 
         tag.reload
 
-        expect(tag.name).to eq('spec_tag')
-        expect(TagName.find_by!(name: 'put_roundtrip_b').canonical).to eq(tag.tag_name)
-        expect(tag.tag_name.aliases.map(&:name)).to contain_exactly('put_roundtrip_b', 'unko')
-        expect(tag.tag_name.aliases.map(&:name)).not_to include('spec_tag')
-        expect(alias_tn.reload.canonical).to eq(tag.tag_name)
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('spec_tag')
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_roundtrip_b'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
+        expect(TagName.where(tag_id: tag.id, language_code: 'ja', primary_flg: false).pluck(:name))
+            .to contain_exactly('put_roundtrip_b', 'unko')
+        expect(TagName.where(tag_id: tag.id, language_code: 'ja', primary_flg: false).pluck(:name))
+            .not_to include('spec_tag')
+        expect(alias_tn.reload).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: false)
 
         version = tag.tag_versions.order(:version_no).last
 
         expect(version.event_type).to eq('update')
-        expect(version.name).to eq('spec_tag')
-        expect(version.aliases.split).to contain_exactly('put_roundtrip_b', 'unko')
+        expect(version_primary_name(version, 'ja')).to eq('spec_tag')
+        expect(version_alias_names(version, 'ja')).to contain_exactly('put_roundtrip_b', 'unko')
       end
 
       it 'parent tag の snapshot も作成する' do
-        old_parent = Tag.create!(
-          tag_name: TagName.create!(name: 'put_snapshot_old_parent'),
-          category: :general
-        )
-        new_parent = Tag.create!(
-          tag_name: TagName.create!(name: 'put_snapshot_new_parent'),
-          category: :general
-        )
+        old_parent = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'put_snapshot_old_parent'),
+            category: :general)
+        new_parent = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'put_snapshot_new_parent'),
+            category: :general)
         TagImplication.create!(tag:, parent_tag: old_parent)
 
         put "/tags/#{ tag.id }", params: {
           name: 'spec_tag',
           category: 'general',
           aliases: 'unko',
-          parent_tags: new_parent.name,
+          parent_tags: primary_tag_name_for(new_parent, 'ja').name,
           deprecated: '0',
         }
 
@@ -1347,13 +1355,13 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(response).to have_http_status(:unprocessable_entity)
 
-        expect(tag.reload.name).to eq('spec_tag')
+        expect(primary_tag_name_for(tag.reload, 'ja').name).to eq('spec_tag')
         expect(tag.category).to eq('general')
       end
 
       it 'system tag の name は変更できない' do
         system_tag = Tag.tagme
-        old_name = system_tag.name
+        old_name = primary_tag_name_for(system_tag, 'ja').name
         old_category = system_tag.category
 
         expect {
@@ -1368,14 +1376,14 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(response).to have_http_status(:unprocessable_entity)
 
-        expect(system_tag.reload.name).to eq(old_name)
+        expect(primary_tag_name_for(system_tag.reload, 'ja').name).to eq(old_name)
         expect(system_tag.category).to eq(old_category)
       end
 
       it 'wiki を持つ tag を更新すると wiki version も作成する' do
         wiki_page =
             Wiki::Commit.create_content!(
-                tag_name: tag.tag_name,
+                tag_name: primary_tag_name_for(tag, 'ja'),
                 body: 'wiki body before',
                 created_by_user: member_user,
                 message: 'init')
@@ -1411,10 +1419,10 @@ RSpec.describe 'Tags API', type: :request do
         )
       end
 
-      it 'wiki を持つ tag を旧 alias へ戻しても wiki を新 canonical へ移す' do
+      it 'wiki を持つ tag を旧 alias へ戻しても wiki を新しい正本名へ移す' do
         wiki_page =
             Wiki::Commit.create_content!(
-                tag_name: tag.tag_name,
+                tag_name: primary_tag_name_for(tag, 'ja'),
                 body: 'wiki body before',
                 created_by_user: member_user,
                 message: 'init')
@@ -1443,9 +1451,11 @@ RSpec.describe 'Tags API', type: :request do
 
         tag.reload
 
-        expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
-        expect(TagName.find_by!(name: 'put_wiki_roundtrip_b').wiki_page).to be_nil
-        expect(TagName.find_by!(name: 'put_wiki_roundtrip_b').canonical).to eq(tag.tag_name)
+        expect(wiki_page.reload.tag_name).to eq(primary_tag_name_for(tag, 'ja'))
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_wiki_roundtrip_b').wiki_page)
+            .to be_nil
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_wiki_roundtrip_b'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
 
         versions = wiki_page.wiki_versions.order(:version_no).last(2)
 
@@ -1454,16 +1464,16 @@ RSpec.describe 'Tags API', type: :request do
       end
 
       it '別名を他 tag から奪った場合、奪はれた側の tag version も作成する' do
-        old_owner = Tag.create!(
-          tag_name: TagName.create!(name: 'put_alias_old_owner'),
-          category: :general
-        )
-        stolen_alias = TagName.create!(
-          name: 'put_stolen_alias',
-          canonical: old_owner.tag_name
-        )
+        old_owner = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'put_alias_old_owner'),
+            category: :general)
+        stolen_alias = create(:tag_name, :alias,
+            name: 'put_stolen_alias',
+            tag: old_owner)
 
-        expect(old_owner.tag_name.aliases.map(&:name)).to include('put_stolen_alias')
+        expect(TagName.where(tag_id: old_owner.id, language_code: 'ja',
+                              primary_flg: false).pluck(:name))
+            .to include('put_stolen_alias')
 
         expect {
           put "/tags/#{ tag.id }", params: {
@@ -1479,30 +1489,32 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(response).to have_http_status(:ok)
 
-        expect(stolen_alias.reload.canonical).to eq(tag.tag_name)
-        expect(old_owner.reload.tag_name.aliases.map(&:name)).not_to include('put_stolen_alias')
+        expect(stolen_alias.reload).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: false)
+        expect(TagName.where(tag_id: old_owner.id, language_code: 'ja',
+                              primary_flg: false).pluck(:name))
+            .not_to include('put_stolen_alias')
 
         old_owner_versions = old_owner.tag_versions.order(:version_no)
 
         expect(old_owner_versions.first.event_type).to eq('create')
-        expect(old_owner_versions.first.aliases.split).to include('put_stolen_alias')
+        expect(version_alias_names(old_owner_versions.first, 'ja')).to include('put_stolen_alias')
 
         expect(old_owner_versions.second.event_type).to eq('update')
-        expect(old_owner_versions.second.aliases.split).not_to include('put_stolen_alias')
+        expect(version_alias_names(old_owner_versions.second, 'ja'))
+            .not_to include('put_stolen_alias')
       end
 
       it '別 tag の alias 名を rename で奪へる' do
-        old_owner = Tag.create!(
-          tag_name: TagName.create!(name: 'put_alias_collision_owner'),
-          category: :general
-        )
-        stolen_alias = TagName.create!(
-          name: 'put_alias_collision_name',
-          canonical: old_owner.tag_name
-        )
+        old_owner = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'put_alias_collision_owner'),
+            category: :general)
+        stolen_alias = create(:tag_name, :alias,
+            name: 'put_alias_collision_name',
+            tag: old_owner)
         wiki_page =
             Wiki::Commit.create_content!(
-                tag_name: tag.tag_name,
+                tag_name: primary_tag_name_for(tag, 'ja'),
                 body: 'put collision wiki',
                 created_by_user: member_user,
                 message: 'init')
@@ -1515,29 +1527,33 @@ RSpec.describe 'Tags API', type: :request do
           deprecated: '0',
         }
 
-        expect(response).to have_http_status(:ok)
+        expect(response).to have_http_status(:ok), response.body
 
         tag.reload
         old_owner.reload
         stolen_alias.reload
 
-        expect(tag.name).to eq('put_alias_collision_name')
-        expect(stolen_alias.canonical_id).to be_nil
-        expect(TagName.find_by!(name: 'spec_tag').canonical).to eq(tag.tag_name)
-        expect(old_owner.tag_name.aliases.map(&:name)).not_to include('put_alias_collision_name')
+        expect(primary_tag_name_for(tag, 'ja').name).to eq('put_alias_collision_name')
+        expect(stolen_alias).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: true)
+        expect(TagName.find_by!(language_code: 'ja', name: 'spec_tag'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
+        expect(TagName.where(tag_id: old_owner.id, language_code: 'ja',
+                              primary_flg: false).pluck(:name))
+            .not_to include('put_alias_collision_name')
 
         old_owner_versions = old_owner.tag_versions.order(:version_no)
 
         expect(old_owner_versions.last.event_type).to eq('update')
-        expect(old_owner_versions.last.aliases.split).not_to include('put_alias_collision_name')
-        expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
+        expect(version_alias_names(old_owner_versions.last, 'ja'))
+            .not_to include('put_alias_collision_name')
+        expect(wiki_page.reload.tag_name).to eq(primary_tag_name_for(tag, 'ja'))
       end
 
       it 'parent_tags に指定すると循環する tag は 422 にする' do
-        child = Tag.create!(
-          tag_name: TagName.create!(name: 'put_cycle_child'),
-          category: :general
-        )
+        child = create(:tag,
+            primary_tag_name: create(:tag_name, name: 'put_cycle_child'),
+            category: :general)
 
         TagImplication.create!(tag: child, parent_tag: tag)
 
@@ -1545,7 +1561,7 @@ RSpec.describe 'Tags API', type: :request do
           name: 'spec_tag',
           category: 'general',
           aliases: 'unko',
-          parent_tags: child.name,
+          parent_tags: primary_tag_name_for(child, 'ja').name,
           deprecated: '0',
         }
 
@@ -1557,7 +1573,7 @@ RSpec.describe 'Tags API', type: :request do
       it 'tag の name を変更すると対応する wiki version を作成する' do
         wiki_page =
             Wiki::Commit.create_content!(
-                tag_name: tag.tag_name,
+                tag_name: primary_tag_name_for(tag, 'ja'),
                 body: 'wiki body before',
                 created_by_user: member_user,
                 message: 'init')
diff --git a/backend/spec/requests/theatres_spec.rb b/backend/spec/requests/theatres_spec.rb
index 7fd3a0a..60fb964 100644
--- a/backend/spec/requests/theatres_spec.rb
+++ b/backend/spec/requests/theatres_spec.rb
@@ -396,7 +396,7 @@ RSpec.describe 'Theatres API', type: :request do
     end
 
     it 'finalizes skip when votes reach majority and stores voters and tag snapshots' do
-      tag = create(:tag, name: 'skip-target')
+      tag = create(:tag, primary_name: 'skip-target')
       PostTag.create!(post: niconico_post, tag:)
 
       TheatreSkipVote.create!(theatre:, post: niconico_post, user: member)
@@ -503,7 +503,7 @@ RSpec.describe 'Theatres API', type: :request do
     end
 
     it 'returns tag penalties and candidate weights for the current watchers' do
-      tag = create(:tag, name: 'heavy-tag')
+      tag = create(:tag, primary_name: 'heavy-tag')
       PostTag.create!(post: second_niconico_post, tag:)
       event = TheatreSkipEvent.create!(
         theatre:,
diff --git a/backend/spec/requests/wiki_conflict_spec.rb b/backend/spec/requests/wiki_conflict_spec.rb
index 9ae9052..39c5458 100644
--- a/backend/spec/requests/wiki_conflict_spec.rb
+++ b/backend/spec/requests/wiki_conflict_spec.rb
@@ -10,7 +10,7 @@ RSpec.describe 'Wiki conflict handling', type: :request do
   it 'returns 409 when base_revision_id is stale' do
     page =
         Wiki::Commit.create_content!(
-            tag_name: TagName.create!(name: 'wiki_conflict_request'),
+            tag_name: create(:tag_name, name: 'wiki_conflict_request'),
             body: 'first',
             created_by_user: user,
             message: 'init')
diff --git a/backend/spec/requests/wiki_history_integrity_spec.rb b/backend/spec/requests/wiki_history_integrity_spec.rb
index 7f2ccce..db365c6 100644
--- a/backend/spec/requests/wiki_history_integrity_spec.rb
+++ b/backend/spec/requests/wiki_history_integrity_spec.rb
@@ -10,7 +10,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
 
   def create_wiki_page title:, body: 'body', message: 'init', user: self.user
     Wiki::Commit.create_content!(
-        tag_name: TagName.create!(name: title),
+        tag_name: create(:tag_name, name: title),
         body:,
         created_by_user: user,
         message:)
diff --git a/backend/spec/requests/wiki_spec.rb b/backend/spec/requests/wiki_spec.rb
index 614180e..e1d31b1 100644
--- a/backend/spec/requests/wiki_spec.rb
+++ b/backend/spec/requests/wiki_spec.rb
@@ -10,7 +10,7 @@ RSpec.describe 'Wiki API', type: :request do
 
   let!(:user) { create_member_user! }
 
-  let!(:tn) { TagName.create!(name: 'spec_wiki_title') }
+  let!(:tn) { create(:tag_name, name: 'spec_wiki_title') }
   let!(:page) do
     Wiki::Commit.create_content!(
         tag_name: tn,
@@ -19,11 +19,10 @@ RSpec.describe 'Wiki API', type: :request do
         message: 'init')
   end
   let!(:tag) do
-    Tag.create!(
-      tag_name: tn,
-      category: :general,
-      deprecated_at: Time.zone.local(2026, 6, 1)
-    )
+    create(:tag,
+        primary_tag_name: tn,
+        category: :general,
+        deprecated_at: Time.zone.local(2026, 6, 1))
   end
 
   describe 'GET /wiki' do
@@ -208,7 +207,7 @@ RSpec.describe 'Wiki API', type: :request do
       { 'X-Transfer-Code' => user.inheritance_code }
     end
 
-    let!(:test_tag_name) { TagName.create!(name: 'TestPage') }
+    let!(:test_tag_name) { create(:tag_name, name: 'TestPage') }
 
     let!(:page) do
       Wiki::Commit.create_content!(
@@ -275,8 +274,8 @@ RSpec.describe 'Wiki API', type: :request do
       end
 
       it 'wiki body だけを変更しても tag version は作成しない' do
-        linked_tag_name = TagName.create!(name: 'wiki_body_only_tag')
-        linked_tag = Tag.create!(tag_name: linked_tag_name, category: :general)
+        linked_tag_name = create(:tag_name, name: 'wiki_body_only_tag')
+        linked_tag = create(:tag, primary_tag_name: linked_tag_name, category: :general)
 
         TagVersionRecorder.record!(
             tag: linked_tag,
@@ -359,13 +358,13 @@ RSpec.describe 'Wiki API', type: :request do
   describe 'GET /wiki/search' do
     before do
       Wiki::Commit.create_content!(
-          tag_name: TagName.create!(name: 'spec_wiki_title_2'),
+          tag_name: create(:tag_name, name: 'spec_wiki_title_2'),
           body: 'search body 2',
           created_by_user: user,
           message: 'init')
 
       Wiki::Commit.create_content!(
-          tag_name: TagName.create!(name: 'unrelated_title'),
+          tag_name: create(:tag_name, name: 'unrelated_title'),
           body: 'unrelated body',
           created_by_user: user,
           message: 'init')
@@ -434,7 +433,7 @@ RSpec.describe 'Wiki API', type: :request do
 
     it 'returns empty array when page has no revisions and filtered by id' do
       # 別ページを作って revision 無し
-      tn2 = TagName.create!(name: 'spec_no_rev')
+      tn2 = create(:tag_name, name: 'spec_no_rev')
       # 異常データ: revision 無し WikiPage を直接作る
       p2 = WikiPage.create!(
           tag_name: tn2,
@@ -514,7 +513,7 @@ RSpec.describe 'Wiki API', type: :request do
 
   describe 'Wiki::Commit.redirect!' do
     it 'raises because redirect revisions are deprecated' do
-      target_tag_name = TagName.create!(name: 'redirect_deprecated_target')
+      target_tag_name = create(:tag_name, name: 'redirect_deprecated_target')
       target =
           Wiki::Commit.create_content!(
               tag_name: target_tag_name,
@@ -535,8 +534,8 @@ RSpec.describe 'Wiki API', type: :request do
   end
 
   it 'wiki title を変更すると対応する tag の version を作成する' do
-    linked_tag_name = TagName.create!(name: 'wiki_linked_tag_for_version')
-    linked_tag = Tag.create!(tag_name: linked_tag_name, category: :general)
+    linked_tag_name = create(:tag_name, name: 'wiki_linked_tag_for_version')
+    linked_tag = create(:tag, primary_tag_name: linked_tag_name, category: :general)
 
     linked_page =
         Wiki::Commit.create_content!(
@@ -564,7 +563,8 @@ RSpec.describe 'Wiki API', type: :request do
     expect(response).to have_http_status(:ok)
 
     linked_tag.reload
-    expect(linked_tag.name).to eq('wiki_linked_tag_for_version_renamed')
+    expect(primary_tag_name_for(linked_tag, 'ja').name)
+        .to eq('wiki_linked_tag_for_version_renamed')
 
     versions = linked_tag.tag_versions.order(:version_no)
 
diff --git a/backend/spec/requests/wiki_title_collision_spec.rb b/backend/spec/requests/wiki_title_collision_spec.rb
index ad02dfa..f78f987 100644
--- a/backend/spec/requests/wiki_title_collision_spec.rb
+++ b/backend/spec/requests/wiki_title_collision_spec.rb
@@ -9,7 +9,7 @@ RSpec.describe 'Wiki title collision', type: :request do
 
   def create_wiki_page title:, body:
     Wiki::Commit.create_content!(
-        tag_name: TagName.create!(name: title),
+        tag_name: create(:tag_name, name: title),
         body:,
         created_by_user: user,
         message: 'init')
diff --git a/backend/spec/services/material_sync_importer_spec.rb b/backend/spec/services/material_sync_importer_spec.rb
index 20c69fd..b2734e3 100644
--- a/backend/spec/services/material_sync_importer_spec.rb
+++ b/backend/spec/services/material_sync_importer_spec.rb
@@ -2,7 +2,7 @@ require 'rails_helper'
 
 RSpec.describe MaterialSyncImporter do
   let(:user) { create(:user, :member) }
-  let(:tag) { Tag.create!(tag_name: TagName.create!(name: 'sync_tag'), category: :material) }
+  let(:tag) { create(:tag, primary_name: 'sync_tag', category: :material) }
 
   def tempfile_for body
     Tempfile.new(['material-sync-importer', '.png']).tap do |file|
diff --git a/backend/spec/services/nico_tag_version_recorder_spec.rb b/backend/spec/services/nico_tag_version_recorder_spec.rb
index e90d1e6..e48745b 100644
--- a/backend/spec/services/nico_tag_version_recorder_spec.rb
+++ b/backend/spec/services/nico_tag_version_recorder_spec.rb
@@ -65,7 +65,7 @@ RSpec.describe NicoTagVersionRecorder do
   end
 
   it 'records sorted linked internal names and later link removal' do
-    tags = ['z_link', 'a_link'].map { |name| Tag.create!(name:, category: :general) }
+    tags = ['z_link', 'a_link'].map { |name| create(:tag, primary_name: name, category: :general) }
     tags.each { |tag| NicoTagRelation.create!(nico_tag: external_tag, tag:) }
 
     expect(record(:create).linked_tags).to eq('a_link z_link')
diff --git a/backend/spec/services/post_bulk_creator_spec.rb b/backend/spec/services/post_bulk_creator_spec.rb
index 0779661..d5167bb 100644
--- a/backend/spec/services/post_bulk_creator_spec.rb
+++ b/backend/spec/services/post_bulk_creator_spec.rb
@@ -1,7 +1,10 @@
 require 'rails_helper'
 
 RSpec.describe PostBulkCreator do
+  include_context 'English locale'
+
   it 'limits workers to two and keeps failures in their request slots' do
+    locale = Locale.nipponese
     actor = instance_double(User, id: 123)
     allow(User).to receive(:find).with(123) {
       instance_double(User, id: 123)
@@ -9,6 +12,7 @@ RSpec.describe PostBulkCreator do
     mutex = Mutex.new
     active = 0
     maximum_active = 0
+    creators = []
 
     allow(PostCreatePreflight).to receive(:new) do |attributes:, **|
       preflight = instance_double(PostCreatePreflight)
@@ -28,6 +32,7 @@ RSpec.describe PostBulkCreator do
     end
     allow(PostCreator).to receive(:new) do |attributes:, **|
       creator = instance_double(PostCreator)
+      mutex.synchronize { creators << creator }
       if attributes[:title] == 'broken'
         allow(creator).to receive(:create!).and_raise(StandardError, 'broken')
       else
@@ -45,7 +50,12 @@ RSpec.describe PostBulkCreator do
     results = described_class.new(
         actor:,
         posts:,
-        thumbnails: { }).run.fetch(:results)
+        thumbnails: { }).run(locale).fetch(:results)
+
+    expect(creators.length).to eq(posts.length)
+    creators.each do |creator|
+      expect(creator).to have_received(:create!).with(locale).once
+    end
 
     expect(maximum_active).to eq(2)
     expect(results.length).to eq(posts.length)
@@ -56,4 +66,26 @@ RSpec.describe PostBulkCreator do
     expect(results[2].dig(:post, :id)).to eq(3)
     expect(results[3].dig(:post, :id)).to eq(4)
   end
+
+  it 'passes a future English locale to preflight and creation in every worker' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    locale
+    actor = instance_double(User, id: 123)
+    allow(User).to receive(:find).with(123).and_return(actor)
+    preflight = instance_double(PostCreatePreflight)
+    creator = instance_double(PostCreator)
+    post = instance_double(Post, id: 1)
+    allow(PostCreatePreflight).to receive(:new).and_return(preflight)
+    allow(preflight).to receive(:run).with(locale).and_return(existing_post_id: nil)
+    allow(PostCreator).to receive(:new).and_return(creator)
+    allow(creator).to receive(:create!).with(locale).and_return(post)
+
+    results = described_class.new(
+        actor:, posts: [{ title: 'future post' }], thumbnails: { }).run(locale)
+
+    expect(results.fetch(:results)).to contain_exactly(
+        hash_including(status: 'created', post: { id: 1 }))
+    expect(preflight).to have_received(:run).with(locale).once
+    expect(creator).to have_received(:create!).with(locale).once
+  end
 end
diff --git a/backend/spec/services/post_create_plan_spec.rb b/backend/spec/services/post_create_plan_spec.rb
index 71a19c1..7d190ab 100644
--- a/backend/spec/services/post_create_plan_spec.rb
+++ b/backend/spec/services/post_create_plan_spec.rb
@@ -2,7 +2,7 @@ require 'rails_helper'
 
 RSpec.describe PostCreatePlan do
   def create_tag! name, category
-    Tag.create!(name:, category:)
+    create(:tag, primary_name: name, category:)
   end
 
   before do
@@ -10,6 +10,63 @@ RSpec.describe PostCreatePlan do
     create_tag!('ニジラー情報不詳', :meta)
   end
 
+  context 'with an explicit locale' do
+    include_context 'English locale'
+
+    it 'resolves the matching language identity and its parents' do
+      pending '日本語以外の Locale 有効化は別課題で実装する'
+      locale
+      english_name = create(:tag_name, name: 'shared_name',
+                                      language_code: 'en', script_code: 'Latn')
+      english = create(:tag, primary_tag_name: english_name, category: :character)
+      nipponese = create(:tag, primary_name: 'temporary_nipponese', category: :general)
+      # The DB permits this identity; validation has its own contract spec.
+      primary_tag_name_for(nipponese, 'ja').update_columns(name: 'shared_name')
+      english_parent_name = create(:tag_name, name: 'english_parent',
+                                            language_code: 'en', script_code: 'Latn')
+      english_parent = create(:tag, primary_tag_name: english_parent_name,
+                                    category: :material)
+      nipponese_parent = create(:tag, primary_name: 'nipponese_parent', category: :general)
+      TagImplication.create!(tag: english, parent_tag: english_parent)
+      TagImplication.create!(tag: nipponese, parent_tag: nipponese_parent)
+
+      plan = described_class.new(attributes: { tags: 'shared_name' }).build!(locale)
+
+      expect(plan[:direct_tag_specs]).to eq(
+          [{ name: 'shared_name', category: :character }])
+      expect(plan[:post_tag_specs]).to include(
+          { name: primary_tag_name_for(english_parent, 'en').name, category: :material })
+      expect(plan[:post_tag_specs].pluck(:name))
+          .not_to include(primary_tag_name_for(nipponese_parent, 'ja').name)
+    end
+
+    it 'resolves aliases within 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, category: :character)
+      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')
+
+      plan = described_class.new(attributes: { tags: 'shared_alias' }).build!(locale)
+
+      expect(plan[:direct_tag_specs]).to eq(
+          [{ name: english_name.name, category: :character }])
+    end
+  end
+
   it 'plans direct and existing default tags without persisting records' do
     counts = [TagName.count, Tag.count]
 
@@ -18,7 +75,7 @@ RSpec.describe PostCreatePlan do
             url: 'https://example.com/post',
             title: 'title',
             tags: 'character:new_character',
-            parent_post_ids: '' }).build!
+            parent_post_ids: '' }).build!(Locale.nipponese)
 
     expect(plan[:tags]).to eq('new_character')
     expect(plan[:direct_tag_specs]).to eq(
@@ -29,9 +86,9 @@ RSpec.describe PostCreatePlan do
     expect([TagName.count, Tag.count]).to eq(counts)
   end
 
-  it 'resolves aliases and keeps tag sections separate from canonical names' do
-    canonical = create_tag!('虹夏', :character)
-    TagName.create!(name: 'にじか', canonical: canonical.tag_name)
+  it 'resolves aliases and keeps tag sections separate from primary names' do
+    tag = create_tag!('虹夏', :character)
+    create(:tag_name, :alias, name: 'にじか', tag:)
     create_tag!('動画', :meta)
 
     plan = described_class.new(
@@ -40,7 +97,7 @@ RSpec.describe PostCreatePlan do
             title: 'video',
             tags: '動画 にじか[0:10-0:20]',
             duration: '1:00',
-            parent_post_ids: '' }).build!
+            parent_post_ids: '' }).build!(Locale.nipponese)
 
     expect(plan[:tags].split).to include('動画', '虹夏[0:10-0:20]')
     expect(plan[:display_tags]).to include(
@@ -55,7 +112,7 @@ RSpec.describe PostCreatePlan do
     counts = [Tag.count, TagName.count, ExternalTag.count]
 
     expect {
-      described_class.new(attributes: { tags: 'NiCo:reserved' }).build!
+      described_class.new(attributes: { tags: 'NiCo:reserved' }).build!(Locale.nipponese)
     }.to raise_error(ActiveRecord::RecordInvalid) { |error|
       expect(error.record.errors[:tags]).to be_present
     }
@@ -73,7 +130,7 @@ RSpec.describe PostCreatePlan do
               url: 'https://example.com/post',
               title: 'title',
               tags: long_name,
-              parent_post_ids: '' }).build!
+              parent_post_ids: '' }).build!(Locale.nipponese)
     }.to raise_error(ActiveRecord::RecordInvalid) { |error|
       expect(error.record.errors[:tags]).not_to be_empty
     }
@@ -87,7 +144,7 @@ RSpec.describe PostCreatePlan do
             title: 'title',
             tags: 'ordinary_tag',
             duration: 'invalid',
-            parent_post_ids: '' }).build!
+            parent_post_ids: '' }).build!(Locale.nipponese)
 
     expect(plan[:duration]).to eq('invalid')
     expect(plan[:video_ms]).to be_nil
diff --git a/backend/spec/services/post_creator_spec.rb b/backend/spec/services/post_creator_spec.rb
index cadf8a1..624577d 100644
--- a/backend/spec/services/post_creator_spec.rb
+++ b/backend/spec/services/post_creator_spec.rb
@@ -14,7 +14,6 @@ RSpec.describe PostCreator do
   end
 
   before do
-    allow(Tag).to receive(:normalise_tags!).and_return({ tags: [], sections: {} })
     allow(TagVersioning).to receive(:record_tag_snapshots!)
     allow(Tag).to receive(:expand_parent_tags).and_return([])
     allow(PostVersionRecorder).to receive(:record!)
@@ -34,7 +33,7 @@ RSpec.describe PostCreator do
           url: 'https://example.com/post',
           thumbnail: real_thumbnail_upload,
           thumbnail_base: 'https://example.com/thumb.jpg',
-          tags: '' }).create!
+          tags: '' }).create!(Locale.nipponese)
 
     expect(post.thumbnail).to be_attached
     expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
@@ -54,7 +53,7 @@ RSpec.describe PostCreator do
           title: 'title',
           url: 'https://example.com/post',
           thumbnail_base: 'https://example.com/thumb.jpg',
-          tags: '' }).create!
+          tags: '' }).create!(Locale.nipponese)
 
     expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
     expect(post.thumbnail).to be_attached
@@ -72,7 +71,36 @@ RSpec.describe PostCreator do
           tags: '' })
 
     post_count = Post.count
-    expect { creator.create! }.to raise_error(Post::RemoteThumbnailFetchFailed)
+    expect { creator.create!(Locale.nipponese) }
+        .to raise_error(Post::RemoteThumbnailFetchFailed)
     expect(Post.count).to eq(post_count)
   end
+
+  context 'with an explicit locale' do
+    include_context 'English locale'
+
+    [false, true].each do |planned|
+      it "passes locale to tag creation with planned attributes: #{ planned }" do
+        pending '日本語以外の Locale 有効化は別課題で実装する'
+        locale
+        attributes = {
+            title: 'Locale propagation',
+            url: 'https://example.com/locale-post',
+            tags: 'character:locale_character' }
+        if planned
+          specs = [{ name: 'locale_character', category: :character }]
+          attributes.merge!(snapshot_tag_specs: specs, post_tag_specs: specs)
+        end
+        allow(Tag).to receive(:find_or_create_by_tag_name!).and_call_original
+
+        post = described_class.new(actor:, attributes:).create!(locale)
+
+        expect(Tag).to have_received(:find_or_create_by_tag_name!)
+            .with(locale, 'locale_character', category: :character).at_least(:once)
+        tag_name = TagName.find_by!(language_code: 'en', name: 'locale_character')
+        expect(tag_name).to have_attributes(script_code: 'Latn', primary_flg: true)
+        expect(post.tags).to include(tag_name.tag)
+      end
+    end
+  end
 end
diff --git a/backend/spec/services/post_import_previewer_spec.rb b/backend/spec/services/post_import_previewer_spec.rb
index bd6e267..cb6888b 100644
--- a/backend/spec/services/post_import_previewer_spec.rb
+++ b/backend/spec/services/post_import_previewer_spec.rb
@@ -64,7 +64,7 @@ RSpec.describe PostImportPreviewer do
     end
 
     it 'applies metadata to automatic fields and recognises metadata tags' do
-      Tag.create!(name: 'known-tag', category: :general)
+      create(:tag, primary_name: 'known-tag', category: :general)
       allow(PostMetadataFetcher).to receive(:fetch).and_return(
         title: 'metadata title',
         thumbnail_base: 'https://example.com/thumb.jpg',
diff --git a/backend/spec/services/tag_version_recorder_spec.rb b/backend/spec/services/tag_version_recorder_spec.rb
new file mode 100644
index 0000000..e403ef6
--- /dev/null
+++ b/backend/spec/services/tag_version_recorder_spec.rb
@@ -0,0 +1,101 @@
+require 'rails_helper'
+
+RSpec.describe TagVersionRecorder do
+  include_context 'English locale'
+
+  let(:user) { create_member_user! }
+  let!(:tag) { create(:tag, primary_name: '日本語名') }
+
+  before do
+    create(:tag_name, :alias, tag:, name: 'alias_z')
+    create(:tag_name, :alias, tag:, name: 'alias_a')
+  end
+
+  def nipponese_snapshot
+    { 'name' => '日本語名', 'script_code' => 'Jpan', 'auto_generated' => false,
+      'aliases' => [{ 'name' => 'alias_a', 'script_code' => 'Jpan' },
+                    { 'name' => 'alias_z', 'script_code' => 'Jpan' }] }
+  end
+
+  def prepare_english_names!
+    locale
+    primary_tag_name_for(tag, 'en').update!(name: 'English name', auto_generated: false)
+    create(:tag_name, :alias, tag:, language_code: 'en', script_code: 'Latn',
+                              name: 'English alias')
+  end
+
+  it 'snapshots the Nipponese primary and sorted aliases in grouped names' do
+    version = described_class.record!(tag:, event_type: :create, created_by_user: user)
+
+    expect(version.reload.names).to eq('ja' => nipponese_snapshot)
+  end
+
+  it 'does not create a version for an unchanged Nipponese snapshot' do
+    original = described_class.record!(tag:, event_type: :create, created_by_user: user)
+
+    unchanged = described_class.record!(tag:, event_type: :update, created_by_user: user)
+
+    expect(unchanged.version_no).to eq(original.version_no)
+    expect(tag.reload.tag_versions.count).to eq(1)
+  end
+
+  it 'snapshots an unconfirmed system primary with auto_generated true' do
+    primary_tag_name_for(tag, 'ja').update!(auto_generated: true)
+
+    version = described_class.record!(tag:, event_type: :create, created_by_user: user)
+
+    expect(version.names.fetch('ja')).to eq(nipponese_snapshot.merge('auto_generated' => true))
+  end
+
+  it 'keeps a past snapshot after current primary and alias changes' do
+    original = described_class.record!(tag:, event_type: :create, created_by_user: user)
+    primary_tag_name_for(tag, 'ja').update!(name: '改名後')
+    tag.tag_names.find_by!(name: 'alias_z').destroy!
+
+    updated = described_class.record!(tag:, event_type: :update, created_by_user: user)
+
+    expect(original.reload.names).to eq('ja' => nipponese_snapshot)
+    expect(updated.names.fetch('ja')).to include('name' => '改名後')
+    expect(updated.names.fetch('ja').fetch('aliases'))
+        .to eq([{ 'name' => 'alias_a', 'script_code' => 'Jpan' }])
+    expect(updated.version_no).to eq(2)
+  end
+
+  it 'snapshots future languages together without a request locale argument' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    prepare_english_names!
+
+    version = described_class.record!(tag:, event_type: :create, created_by_user: user)
+
+    expect(version.names).to eq(
+        'ja' => nipponese_snapshot,
+        'en' => { 'name' => 'English name', 'script_code' => 'Latn',
+                  'auto_generated' => false,
+                  'aliases' => [{ 'name' => 'English alias', 'script_code' => 'Latn' }] })
+  end
+
+  it 'creates a version for an English-only change and preserves prior names' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    prepare_english_names!
+    original = described_class.record!(tag:, event_type: :create, created_by_user: user)
+    primary_tag_name_for(tag, 'en').update!(name: 'Renamed')
+
+    updated = described_class.record!(tag:, event_type: :update, created_by_user: user)
+
+    expect(updated.version_no).to eq(2)
+    expect(original.reload.names.fetch('en')).to include('name' => 'English name')
+    expect(updated.names.fetch('en')).to include('name' => 'Renamed')
+    expect(updated.names.fetch('ja')).to eq(nipponese_snapshot)
+  end
+
+  it 'does not create a version for an unchanged multilingual snapshot' do
+    pending '日本語以外の Locale 有効化は別課題で実装する'
+    prepare_english_names!
+    described_class.record!(tag:, event_type: :create, created_by_user: user)
+
+    unchanged = described_class.record!(tag:, event_type: :update, created_by_user: user)
+
+    expect(unchanged.version_no).to eq(1)
+    expect(tag.reload.tag_versions.count).to eq(1)
+  end
+end
diff --git a/backend/spec/services/wiki/commit_integrity_spec.rb b/backend/spec/services/wiki/commit_integrity_spec.rb
index 4a08de5..42c42b7 100644
--- a/backend/spec/services/wiki/commit_integrity_spec.rb
+++ b/backend/spec/services/wiki/commit_integrity_spec.rb
@@ -6,7 +6,7 @@ RSpec.describe Wiki::Commit do
 
   def create_page title:, body: 'initial body'
     described_class.create_content!(
-        tag_name: TagName.create!(name: title),
+        tag_name: create(:tag_name, name: title),
         body:,
         created_by_user: user,
         message: 'init')
@@ -16,7 +16,7 @@ RSpec.describe Wiki::Commit do
     it 'creates page, revision, and version with normalised body' do
       expect {
         described_class.create_content!(
-            tag_name: TagName.create!(name: 'commit_integrity_create'),
+            tag_name: create(:tag_name, name: 'commit_integrity_create'),
             body: "a\r\nb\r\n\r\n",
             created_by_user: user,
             message: 'init')
@@ -36,7 +36,7 @@ RSpec.describe Wiki::Commit do
     end
 
     it 'rejects body that becomes blank after normalisation' do
-      tag_name = TagName.create!(name: 'commit_integrity_blank')
+      tag_name = create(:tag_name, name: 'commit_integrity_blank')
 
       expect {
         described_class.create_content!(
@@ -76,8 +76,8 @@ RSpec.describe Wiki::Commit do
     end
 
     it 'does not record tag_version on body-only wiki update' do
-      tag_name = TagName.create!(name: 'commit_integrity_linked_tag')
-      tag = Tag.create!(tag_name:, category: :general)
+      tag_name = create(:tag_name, name: 'commit_integrity_linked_tag')
+      tag = create(:tag, primary_tag_name: tag_name, category: :general)
 
       page =
           described_class.create_content!(
diff --git a/backend/spec/services/wiki/commit_spec.rb b/backend/spec/services/wiki/commit_spec.rb
index 2e564cf..122ac58 100644
--- a/backend/spec/services/wiki/commit_spec.rb
+++ b/backend/spec/services/wiki/commit_spec.rb
@@ -4,7 +4,7 @@ RSpec.describe Wiki::Commit do
   let(:user) { create_member_user! }
 
   def create_page(title: 'commit_spec_page', body: 'initial body')
-    tag_name = TagName.create!(name: title)
+    tag_name = create(:tag_name, name: title)
 
     Wiki::Commit.create_content!(
         tag_name:,
@@ -80,8 +80,8 @@ RSpec.describe Wiki::Commit do
     end
 
     it 'does not record tag version when corresponding tag has no versions' do
-      tag_name = TagName.create!(name: 'commit_linked_tag_without_versions')
-      tag = Tag.create!(tag_name:, category: :general)
+      tag_name = create(:tag_name, name: 'commit_linked_tag_without_versions')
+      tag = create(:tag, primary_tag_name: tag_name, category: :general)
 
       page =
           described_class.create_content!(
@@ -107,8 +107,8 @@ RSpec.describe Wiki::Commit do
     end
 
     it 'does not record tag version when corresponding tag has no versions' do
-      tag_name = TagName.create!(name: 'commit_linked_tag_without_versions')
-      tag = Tag.create!(tag_name:, category: :general)
+      tag_name = create(:tag_name, name: 'commit_linked_tag_without_versions')
+      tag = create(:tag, primary_tag_name: tag_name, category: :general)
 
       page =
           described_class.create_content!(
diff --git a/backend/spec/services/wiki_version_recorder_spec.rb b/backend/spec/services/wiki_version_recorder_spec.rb
index 9f1c6dd..c8c4dfa 100644
--- a/backend/spec/services/wiki_version_recorder_spec.rb
+++ b/backend/spec/services/wiki_version_recorder_spec.rb
@@ -5,7 +5,7 @@ RSpec.describe WikiVersionRecorder do
 
   def create_page title:, body: 'body'
     Wiki::Commit.create_content!(
-        tag_name: TagName.create!(name: title),
+        tag_name: create(:tag_name, name: title),
         body:,
         created_by_user: user,
         message: 'init')
diff --git a/backend/spec/services/youtube/sync_spec.rb b/backend/spec/services/youtube/sync_spec.rb
index c24c6a1..e8d7a24 100644
--- a/backend/spec/services/youtube/sync_spec.rb
+++ b/backend/spec/services/youtube/sync_spec.rb
@@ -172,7 +172,8 @@ RSpec.describe Youtube::Sync do
       Tag.video
       Tag.no_deerjikist
 
-      deerjikist_tag = Tag.find_or_create_by_tag_name!('テスト投稿者', category: :deerjikist)
+      deerjikist_tag = Tag.find_or_create_by_tag_name!(
+          Locale.nipponese, 'テスト投稿者', category: :deerjikist)
       Deerjikist.create!(
         platform: 'youtube',
         code: 'UC_MAPPED',
@@ -226,7 +227,8 @@ RSpec.describe Youtube::Sync do
       )
       PostTag.create!(post:, tag: Tag.no_deerjikist)
 
-      deerjikist_tag = Tag.find_or_create_by_tag_name!('後から判明した投稿者', category: :deerjikist)
+      deerjikist_tag = Tag.find_or_create_by_tag_name!(
+          Locale.nipponese, '後から判明した投稿者', category: :deerjikist)
       Deerjikist.create!(
         platform: 'youtube',
         code: 'UC_MAPPED_LATER',
diff --git a/backend/spec/support/locale_context.rb b/backend/spec/support/locale_context.rb
new file mode 100644
index 0000000..3241f11
--- /dev/null
+++ b/backend/spec/support/locale_context.rb
@@ -0,0 +1,22 @@
+RSpec.shared_context 'English locale' do
+  def prepare_english_reference!
+    Language.find_or_create_by!(code: 'en') { _1.name = 'English' }
+    Script.find_or_create_by!(code: 'Latn') { _1.name = 'Latin' }
+    region_class = Class.new(ApplicationRecord) { self.table_name = 'regions' }
+    region_class.find_or_create_by!(code: 826) do |record|
+      record.alpha_code = 'GB'
+      record.name = 'United Kingdom'
+    end
+  end
+
+  let(:locale) do
+    prepare_english_reference!
+    Locale.find_or_create_by!(code: 'en') do |record|
+      record.language_code = 'en'
+      record.script_code = 'Latn'
+      record.region_code = 826
+      record.variants = ''
+      record.name = 'English'
+    end
+  end
+end
diff --git a/backend/spec/support/test_records.rb b/backend/spec/support/test_records.rb
index b6a7cd5..a814e68 100644
--- a/backend/spec/support/test_records.rb
+++ b/backend/spec/support/test_records.rb
@@ -1,4 +1,8 @@
 module TestRecords
+  def primary_tag_name_for(tag, language_code)
+    TagName.find_by!(tag_id: tag.id, language_code:, primary_flg: true)
+  end
+
   def create_member_user!
     User.create!(name: 'spec user',
                  inheritance_code: SecureRandom.hex(16),
diff --git a/backend/spec/tasks/nico_sync_spec.rb b/backend/spec/tasks/nico_sync_spec.rb
index b3c053f..db6d55a 100644
--- a/backend/spec/tasks/nico_sync_spec.rb
+++ b/backend/spec/tasks/nico_sync_spec.rb
@@ -8,7 +8,7 @@ RSpec.describe 'nico:sync' do
   end
 
   def create_tag!(name, category:)
-    Tag.find_or_create_by_tag_name!(name, category:)
+    Tag.find_or_create_by_tag_name!(Locale.nipponese, name, category:)
   end
 
   def link_nico_to_tag!(nico_tag, tag)
@@ -16,17 +16,22 @@ RSpec.describe 'nico:sync' do
   end
 
   def create_nico_sanitisation_rules!
-    TagNameSanitisationRule.create!(priority: 20,
-                                    source_pattern: '\\?',
-                                    replacement: '_')
+    rules = [
+        [20, '\\?', '_'],
+        [40, '_$', ''],
+        [45, '^([^:]+\\:)?_', '\\1']]
 
-    TagNameSanitisationRule.create!(priority: 40,
-                                    source_pattern: '_$',
-                                    replacement: '')
+    priorities = rules.map(&:first)
+    source_patterns = rules.map { _1[1] }
 
-    TagNameSanitisationRule.create!(priority: 45,
-                                    source_pattern: '^([^:]+\\:)?_',
-                                    replacement: '\\1')
+    scope = TagNameSanitisationRule.unscoped
+    scope.where(priority: priorities)
+         .or(scope.where(source_pattern: source_patterns))
+         .delete_all
+
+    rules.each do |priority, source_pattern, replacement|
+      TagNameSanitisationRule.create!(priority:, source_pattern:, replacement:)
+    end
   end
 
   it '既存 post を見つけて、nico tag と linked tag を追加し、差分が出たら bot を付ける' do
@@ -64,7 +69,8 @@ RSpec.describe 'nico:sync' do
     run_rake_task('nico:sync')
 
     post.reload
-    active_tag_names = post.tags.joins(:tag_name).pluck('tag_names.name')
+    active_tag_names = TagName.where(tag_id: post.tags.select(:id),
+                                     language_code: 'ja', primary_flg: true).pluck(:name)
 
     expect(active_tag_names).to include('spec_kept')
     expect(post.external_tags).to contain_exactly(nico)
@@ -434,7 +440,9 @@ RSpec.describe 'nico:sync' do
 
     external = post.external_tags.sole
     expect(external.name).to eq('raw tag[]')
-    expect(post.tags.map(&:name)).not_to include('bot操作')
+    expect(TagName.where(tag_id: post.tags.select(:id),
+                         language_code: 'ja', primary_flg: true).pluck(:name))
+        .not_to include('bot操作')
     expect(post.post_versions.order(:version_no).last.tags_json)
         .to include('external_tag_id' => external.id)
 
@@ -446,7 +454,9 @@ RSpec.describe 'nico:sync' do
       run_nico_sync_with_tags!([])
     }.to change(PostVersion, :count).by(1)
     expect(post.reload.external_tags).to be_empty
-    expect(post.tags.map(&:name)).not_to include('bot操作')
+    expect(TagName.where(tag_id: post.tags.select(:id),
+                         language_code: 'ja', primary_flg: true).pluck(:name))
+        .not_to include('bot操作')
   end
 
   it 'サニタイズ後の既存外部タグを再利用し、その連携タグを記載する' do
@@ -563,7 +573,9 @@ RSpec.describe 'nico:sync' do
         name: 'AAA')
     expect(ExternalTag.exists?(platform: :nico, name: 'AAA?')).to be(false)
 
-    expect(post.tags.map(&:name)).not_to include('bot操作')
+    expect(TagName.where(tag_id: post.tags.select(:id),
+                         language_code: 'ja', primary_flg: true).pluck(:name))
+        .not_to include('bot操作')
     expect(post.post_versions.order(:version_no).last.tags_json)
         .to include('external_tag_id' => external.id)
 
@@ -577,7 +589,9 @@ RSpec.describe 'nico:sync' do
     }.to change(PostVersion, :count).by(1)
 
     expect(post.reload.external_tags).to be_empty
-    expect(post.tags.map(&:name)).not_to include('bot操作')
+    expect(TagName.where(tag_id: post.tags.select(:id),
+                         language_code: 'ja', primary_flg: true).pluck(:name))
+        .not_to include('bot操作')
   end
 
   it 'nico: prefix を含む従来の規則で外部タグ名をサニタイズする' do
diff --git a/backend/spec/tasks/post_similarity_calc_spec.rb b/backend/spec/tasks/post_similarity_calc_spec.rb
index 20dd575..721be6c 100644
--- a/backend/spec/tasks/post_similarity_calc_spec.rb
+++ b/backend/spec/tasks/post_similarity_calc_spec.rb
@@ -6,10 +6,10 @@ RSpec.describe 'post_similarity:calc' do
 
   it 'calculates similarities from active tags only' do
     # 必要最低限のデータ
-    t1 = Tag.create!(name: "t1")
-    t2 = Tag.create!(name: "t2")
-    t3 = Tag.create!(name: "t3")
-    deprecated_tag = Tag.create!(name: 'deprecated', deprecated_at: Time.current)
+    t1 = create(:tag, primary_name: 't1')
+    t2 = create(:tag, primary_name: 't2')
+    t3 = create(:tag, primary_name: 't3')
+    deprecated_tag = create(:tag, primary_name: 'deprecated', deprecated_at: Time.current)
 
     p1 = Post.create!(url: "https://example.com/1")
     p2 = Post.create!(url: "https://example.com/2")
diff --git a/backend/spec/tasks/tag_similarity_calc_spec.rb b/backend/spec/tasks/tag_similarity_calc_spec.rb
index 3063010..a5aae72 100644
--- a/backend/spec/tasks/tag_similarity_calc_spec.rb
+++ b/backend/spec/tasks/tag_similarity_calc_spec.rb
@@ -6,10 +6,10 @@ RSpec.describe 'tag_similarity:calc' do
 
   it 'calculates similarities for active tags only' do
     # 必要最低限のデータ
-    t1 = Tag.create!(name: "t1")
-    t2 = Tag.create!(name: "t2")
-    t3 = Tag.create!(name: "t3")
-    deprecated_tag = Tag.create!(name: 'deprecated', deprecated_at: Time.current)
+    t1 = create(:tag, primary_name: 't1')
+    t2 = create(:tag, primary_name: 't2')
+    t3 = create(:tag, primary_name: 't3')
+    deprecated_tag = create(:tag, primary_name: 'deprecated', deprecated_at: Time.current)
 
     p1 = Post.create!(url: "https://example.com/1")
     p2 = Post.create!(url: "https://example.com/2")