#55

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?
@@ -10,7 +12,7 @@ class DeerjikistsController < ApplicationController
                  .includes(tag: :tag_names)
                  .find_by(platform:, code:)
     if deerjikist
-      render json: DeerjikistRepr.base(deerjikist)
+      render json: DeerjikistRepr.base(deerjikist, language_code: locale.language_code)
     else
       head :not_found
     end
@@ -20,6 +22,7 @@ class DeerjikistsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
     tag_id = params[:tag_id].to_i
@@ -32,7 +35,7 @@ class DeerjikistsController < ApplicationController
       d.save!
     end
 
-    render json: DeerjikistRepr.base(deerjikist)
+    render json: DeerjikistRepr.base(deerjikist, language_code: locale.language_code)
   end
 
   def destroy

backend/app/controllers/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
 
@@ -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)
@@ -65,7 +72,8 @@ class MaterialsController < ApplicationController
 
     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
@@ -109,7 +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
@@ -162,7 +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

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
@@ -68,7 +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
 
@@ -109,7 +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

backend/app/controllers/posts_controller.rb

@@ -92,7 +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)
@@ -116,7 +117,7 @@ class PostsController < ApplicationController
         .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
@@ -191,6 +192,8 @@ class PostsController < ApplicationController
   end
 
   def show
+    locale = resolve_locale!
+
     post =
         Post
         .includes(:uploaded_user, :parents, :children,
@@ -209,8 +212,9 @@ class PostsController < ApplicationController
                                  parent_posts:,
                                  child_posts:,
                                  sibling_posts:,
-                                 related:)
+                                 related:,
-                         .merge(tags: build_tag_tree_for(post))
+                                 language_code: locale.language_code)
+                         .merge(tags: build_tag_tree_for(post, locale.language_code))
   end
 
   def create
@@ -251,7 +255,7 @@ class PostsController < ApplicationController
                                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
@@ -379,8 +383,8 @@ class PostsController < ApplicationController
     return render json: conflict_json, status: :conflict if conflict_json
 
     post.reload
-    json = PostRepr.base(post, current_user)
+    json = PostRepr.base(post, current_user, language_code: locale.language_code)
-    json['tags'] = build_tag_tree_for(post)
+    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．'] }
@@ -487,7 +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)
@@ -517,7 +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)
@@ -529,7 +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, []) }

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
@@ -27,12 +28,12 @@ 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
 
@@ -54,13 +55,14 @@ class TagVersionsController < ApplicationController
       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,
+        names: row.names,
         name: { current: row.name, prev: row.attributes['prev_name'] },
         category: { current: row.category, prev: row.attributes['prev_category'] },
         deprecated_at: { current: row.deprecated_at&.iso8601,

backend/app/controllers/tags_controller.rb

@@ -198,7 +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
@@ -325,7 +326,9 @@ class TagsController < ApplicationController
     return head :not_found unless tag
 
     render json: { tag: TagRepr.base(tag, language_code: locale.language_code),
-                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
+                   deerjikists: DeerjikistRepr.many(
+                       tag.deerjikists,
+                       language_code: locale.language_code) }
   end
 
   def deerjikists_by_name
@@ -342,7 +345,9 @@ class TagsController < ApplicationController
     return head :not_found unless tag
 
     render json: { tag: TagRepr.base(tag, language_code: locale.language_code),
-                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
+                   deerjikists: DeerjikistRepr.many(
+                       tag.deerjikists,
+                       language_code: locale.language_code) }
   end
 
   def update_deerjikists
@@ -404,7 +409,8 @@ 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
@@ -422,7 +428,7 @@ class TagsController < ApplicationController
         .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:, language_code: locale.language_code)
   end
@@ -543,9 +549,7 @@ class TagsController < ApplicationController
     value
   end
 
-  def build_with_depth_graph material_filter
+  def build_with_depth_graph material_filter, language_code
-    locale = resolve_locale!
-
     children_by_parent_id = Hash.new { |h, k| h[k] = [] }
     parent_ids_by_child_id = Hash.new { |h, k| h[k] = [] }
 
@@ -564,7 +568,7 @@ class TagsController < ApplicationController
         Tag
         .joins(:tag_names)
         .where(id: tag_ids,
-               tag_names: { language_code: locale.language_code, primary_flg: true })
+               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?,
@@ -712,7 +716,10 @@ class TagsController < ApplicationController
     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:, language_code: 'ja',

backend/app/models/tag_version.rb

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

backend/app/representations/deerjikist_repr.rb

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

backend/app/representations/material_repr.rb

@@ -12,15 +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: 'ja'),
+        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,
@@ -28,11 +28,11 @@ module MaterialRepr
         export_items: export_items(material))
   end
 
-  def many materials, host:
+  def many materials, host:, language_code: 'ja'
-    materials.map { |m| base(m, host:) }
+    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,
@@ -41,9 +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,
@@ -54,8 +54,8 @@ module MaterialRepr
       export_items: export_items(material) }
   end
 
-  def list_many materials, host:
+  def list_many materials, host:, language_code: 'ja'
-    materials.map { |m| list(m, host:) }
+    materials.map { |m| list(m, host:, language_code:) }
   end
 
   def export_paths material
@@ -80,8 +80,8 @@ module MaterialRepr
         material.thumbnail, host:)
   end
 
-  def thumbnail_fallback_text material
+  def thumbnail_fallback_text material, language_code:
-    material.tag&.name('ja') || material.created_at&.strftime('%Y-%m-%d')
+    material.tag&.name(language_code) || material.created_at&.strftime('%Y-%m-%d')
   end
 
   def thumbnail_fallback_kind material
@@ -99,11 +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('ja'),
+      name: tag.name(language_code),
       category: tag.category,
       deprecated_at: tag.deprecated_at }
   end

backend/app/representations/post_repr.rb

@@ -17,23 +17,23 @@ module PostRepr
 
   module_function
 
-  def base post, current_user = nil, host: nil
+  def base post, current_user = nil, host: nil, language_code: 'ja'
     json =
         if host.present?
           common(post, host:)
         else
           common(post)
         end
-    json['tags'] = tag_json(post)
+    json['tags'] = tag_json(post, language_code:)
     json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
     json['viewed'] = current_user ? current_user.viewed?(post) : false
     json
   end
 
   def detail post, current_user = nil, parent_posts: [], child_posts: [],
-             sibling_posts: { }, related: [], host: nil
+             sibling_posts: { }, related: [], host: nil, language_code: 'ja'
     if host.present?
-      base(post, current_user, host:).merge(
+      base(post, current_user, host:, language_code:).merge(
           'parent_posts' => cards(parent_posts, host:),
           'child_posts' => cards(child_posts, host:),
           'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
@@ -41,7 +41,7 @@ module PostRepr
           },
           'related' => cards(related, host:))
     else
-      base(post, current_user).merge(
+      base(post, current_user, language_code:).merge(
           'parent_posts' => cards(parent_posts),
           'child_posts' => cards(child_posts),
           'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
@@ -86,14 +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('ja') }
+        .sort_by { _1.tag.name(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]))
         }

backend/app/services/post_create_preflight.rb

@@ -18,6 +18,7 @@ class PostCreatePreflight
   def run locale
     preview = PostImportPreviewer.new.preview_rows(
         rows: [preview_row],
+        locale:,
         fetch_metadata: false).first
     if preview[:existing_post_id].present?
       return {

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 locale, 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 =
@@ -30,6 +30,7 @@ class PostImportPreviewer
         url_counts)
     known_tags =
         preload_known_tags(
+            locale,
             prepared_rows,
             fetch_metadata,
             metadata_cache,
@@ -347,7 +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)
@@ -359,11 +360,11 @@ 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?
 
-    TagName.where(language_code: 'ja', primary_flg: true, name: names)
+    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

backend/app/services/tag_version_recorder.rb

@@ -1,11 +1,10 @@
 class TagVersionRecorder < VersionRecorder
-  def self.record! tag:, event_type:, created_by_user:, language_code: 'ja'
+  def self.record! tag:, event_type:, created_by_user:, **_options
-    new(tag:, event_type:, created_by_user:, language_code:).record!
+    new(tag:, event_type:, created_by_user:).record!
   end
 
-  def initialize tag:, event_type:, created_by_user:, language_code:
+  def initialize tag:, event_type:, created_by_user:
     super(record: tag, event_type:, created_by_user:)
-    @language_code = language_code
   end
 
   private
@@ -15,10 +14,24 @@ class TagVersionRecorder < VersionRecorder
   def record_key = :tag
 
   def snapshot_attributes
-    { name: @record.name(@language_code),
+    names = snapshot_names
+    japanese_names = names.select { _1[:language_code] == 'ja' }
+    compatibility_names = japanese_names.presence || names
+
+    { name: compatibility_names.find { _1[:primary_flg] }[:name],
       category: @record.category,
       deprecated_at: @record.deprecated_at,
-      aliases: @record.snapshot_aliases(@language_code).join(' '),
+      aliases: compatibility_names.reject { _1[:primary_flg] }.map { _1[:name] }.join(' '),
+      names:,
       parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
   end
+
+  def snapshot_names
+    @record.tag_names.order(:language_code, primary_flg: :desc).order(:name).map { |tag_name|
+      { language_code: tag_name.language_code,
+        name: tag_name.name,
+        script_code: tag_name.script_code,
+        primary_flg: tag_name.primary_flg }
+    }
+  end
 end

backend/db/migrate/20260922040000_add_names_to_tag_versions.rb

@@ -0,0 +1,36 @@
+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|
+        names = [{
+          language_code: 'ja',
+          name: version.name,
+          script_code: 'Jpan',
+          primary_flg: true }]
+        names.concat(version.aliases.to_s.split.filter_map { |name|
+          next if name.blank?
+
+          {
+            language_code: 'ja',
+            name:,
+            script_code: 'Jpan',
+            primary_flg: false }
+        })
+        version.update_columns(names: names)
+      end
+    end
+
+    change_column_null :tag_versions, :names, false
+  end
+
+  def down
+    remove_column :tag_versions, :names
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_09_22_030000) 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
@@ -480,6 +480,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_030000) 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 }

backend/spec/models/version_record_spec.rb

@@ -12,6 +12,8 @@ RSpec.describe VersionRecord, type: :model do
       name: primary_tag_name_for(tag, 'ja').name,
       category: tag.category,
       aliases: '',
+      names: [{ language_code: 'ja', name: primary_tag_name_for(tag, 'ja').name,
+                script_code: 'Jpan', primary_flg: true }],
       parent_tag_ids: '',
       created_at: Time.current,
       created_by_user: nil
@@ -30,6 +32,8 @@ RSpec.describe VersionRecord, type: :model do
       name: primary_tag_name_for(tag, 'ja').name,
       category: tag.category,
       aliases: '',
+      names: [{ language_code: 'ja', name: primary_tag_name_for(tag, 'ja').name,
+                script_code: 'Jpan', primary_flg: true }],
       parent_tag_ids: '',
       created_at: Time.current,
       created_by_user: nil

backend/spec/requests/tag_versions_spec.rb

@@ -36,6 +36,11 @@ RSpec.describe 'TagVersions API', type: :request do
             category: category,
             deprecated_at: deprecated_at,
             aliases: Array(aliases).join(' '),
+            names: [{ language_code: 'ja', name: name, script_code: 'Jpan',
+                      primary_flg: true }] + Array(aliases).map { |alias_name|
+              { language_code: 'ja', name: alias_name, script_code: 'Jpan',
+                primary_flg: false }
+            },
             parent_tag_ids: Array(parent_tags).map(&:id).join(' '),
             created_by_user: created_by_user,
             created_at: created_at)

backend/spec/services/tag_version_recorder_spec.rb

@@ -0,0 +1,47 @@
+require 'rails_helper'
+
+RSpec.describe TagVersionRecorder do
+  let(:user) { create_member_user! }
+  let(:tag) { create(:tag, primary_name: '日本語名') }
+
+  before do
+    Language.insert_all!([{ code: 'en', name: 'English', created_at: Time.current }])
+    Script.insert_all!([{ code: 'Latn', name: 'Latin', created_at: Time.current }])
+    Locale.insert_all!([{ code: 'en', language_code: 'en', script_code: 'Latn',
+                          name: 'English', created_at: Time.current }])
+    TagName.create!(tag:, language_code: 'ja', script_code: 'Jpan', name: '別名',
+                    primary_flg: false,
+                    canonical_id: tag.tag_name_id)
+    TagName.create!(tag:, language_code: 'en', script_code: 'Latn', name: 'English name',
+                    primary_flg: true)
+    TagName.create!(tag:, language_code: 'en', script_code: 'Latn', name: 'English alias',
+                    primary_flg: false)
+  end
+
+  it 'snapshots every language primary name and alias deterministically' do
+    version = described_class.record!(tag:, event_type: :create, created_by_user: user)
+
+    expect(version.names).to eq([
+      { 'language_code' => 'en', 'name' => 'English name', 'script_code' => 'Latn',
+        'primary_flg' => true },
+      { 'language_code' => 'en', 'name' => 'English alias', 'script_code' => 'Latn',
+        'primary_flg' => false },
+      { 'language_code' => 'ja', 'name' => '日本語名', 'script_code' => 'Jpan',
+        'primary_flg' => true },
+      { 'language_code' => 'ja', 'name' => '別名', 'script_code' => 'Jpan',
+        'primary_flg' => false }
+    ])
+  end
+
+  it 'creates a version for an English-only name change and preserves prior names' do
+    original = described_class.record!(tag:, event_type: :create, created_by_user: user)
+    TagName.find_by!(tag:, language_code: 'en', primary_flg: true).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).to include(
+      hash_including('language_code' => 'en', 'name' => 'English name'))
+    expect(updated.names).to include(hash_including('language_code' => 'en', 'name' => 'Renamed'))
+  end
+end