From 5abb6cca98a608299857910559ff0e000dd52145 Mon Sep 17 00:00:00 2001
From: miteruzo <miteruzo@naver.com>
Date: Sat, 26 Sep 2026 20:23:11 +0900
Subject: [PATCH] #55

---
 backend/app/controllers/posts_controller.rb   |   4 +-
 backend/app/services/post_bulk_creator.rb     |   8 +-
 backend/app/services/post_creator.rb          |   2 +-
 backend/db/schema.rb                          |  42 ++-
 backend/spec/factories/tag_names.rb           |  18 +-
 backend/spec/factories/tags.rb                |   5 +
 backend/spec/models/locale_spec.rb            |  69 +++++
 .../spec/models/material_export_item_spec.rb  |   2 +-
 backend/spec/models/post_version_spec.rb      |   4 +-
 .../models/tag_name_sanitisation_rule_spec.rb |  52 +++-
 backend/spec/models/tag_name_spec.rb          |  73 +++++
 backend/spec/models/tag_spec.rb               | 200 +++++++++----
 .../spec/requests/gekanator_learning_spec.rb  |  11 +-
 backend/spec/requests/gekanator_posts_spec.rb |  11 +-
 .../spec/requests/locale_write_paths_spec.rb  | 232 +++++++++++++++
 backend/spec/requests/materials_spec.rb       |  34 +--
 backend/spec/requests/nico_tags_spec.rb       |   8 +-
 backend/spec/requests/posts_spec.rb           | 111 ++++---
 backend/spec/requests/tag_versions_spec.rb    |   4 +-
 .../tag_wiki_history_integrity_spec.rb        |   4 +-
 backend/spec/requests/tags_spec.rb            | 279 ++++++++----------
 backend/spec/requests/wiki_conflict_spec.rb   |   2 +-
 .../requests/wiki_history_integrity_spec.rb   |   2 +-
 backend/spec/requests/wiki_spec.rb            |  29 +-
 .../requests/wiki_title_collision_spec.rb     |   2 +-
 .../services/material_sync_importer_spec.rb   |   2 +-
 .../nico_tag_version_recorder_spec.rb         |   2 +-
 .../spec/services/post_bulk_creator_spec.rb   |  11 +-
 .../spec/services/post_create_plan_spec.rb    |  64 +++-
 backend/spec/services/post_creator_spec.rb    |  34 ++-
 .../services/post_import_previewer_spec.rb    |   2 +-
 .../services/wiki/commit_integrity_spec.rb    |  10 +-
 backend/spec/services/wiki/commit_spec.rb     |  10 +-
 .../services/wiki_version_recorder_spec.rb    |   2 +-
 backend/spec/services/youtube/sync_spec.rb    |   6 +-
 backend/spec/support/locale_context.rb        |  13 +
 backend/spec/tasks/nico_sync_spec.rb          |   2 +-
 .../spec/tasks/post_similarity_calc_spec.rb   |   8 +-
 .../spec/tasks/tag_similarity_calc_spec.rb    |   8 +-
 39 files changed, 1005 insertions(+), 377 deletions(-)
 create mode 100644 backend/spec/models/locale_spec.rb
 create mode 100644 backend/spec/models/tag_name_spec.rb
 create mode 100644 backend/spec/requests/locale_write_paths_spec.rb
 create mode 100644 backend/spec/support/locale_context.rb

diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 73710f4..228cb7b 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -213,6 +213,8 @@ class PostsController < ApplicationController
     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],
@@ -242,7 +244,7 @@ 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
diff --git a/backend/app/services/post_bulk_creator.rb b/backend/app/services/post_bulk_creator.rb
index 1e75e24..e525c57 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,
@@ -61,7 +61,7 @@ class PostBulkCreator
 
   private
 
-  def create_row actor, attributes, index
+  def create_row locale, actor, attributes, index
     preflight =
         PostCreatePreflight.new(
             attributes: attributes,
@@ -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_creator.rb b/backend/app/services/post_creator.rb
index fd834b1..dbe4c89 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!(locale)
+  def create! locale
     thumbnail_attachment = prepare_thumbnail_attachment
     post = Post.new(title: @attributes[:title].presence,
                     url: @attributes[:url],
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index c4ce56a..c6b886b 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_030000) 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 +138,24 @@ 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.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"], name: "index_locales_on_language_code"
+    t.index ["script_code"], name: "fk_rails_0b74ce96a8"
+  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 +406,13 @@ 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 "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"
+  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 +445,20 @@ 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.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"
   end
 
   create_table "tag_similarities", primary_key: ["tag_id", "target_tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -701,6 +734,8 @@ 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", "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 +769,10 @@ 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/factories/tag_names.rb b/backend/spec/factories/tag_names.rb
index a33be1e..4af5bcf 100644
--- a/backend/spec/factories/tag_names.rb
+++ b/backend/spec/factories/tag_names.rb
@@ -1,5 +1,21 @@
 FactoryBot.define do
   factory :tag_name do
-    name { "tag-#{SecureRandom.hex(4)}" }
+    language_code { 'ja' }
+    script_code { 'Jpan' }
+    primary_flg { true }
+    sequence(:name) { |number| "tag-#{ SecureRandom.hex(4) }-#{ number }" }
+
+    trait :alias do
+      primary_flg { false }
+
+      after(:create) do |tag_name|
+        owner = tag_name.canonical&.tag
+        raise ArgumentError, 'alias requires a canonical tag' unless owner
+
+        # The alias validation still rejects tag_id; its contract is tested separately.
+        tag_name.update_columns(tag_id: owner.id)
+        tag_name.association(:tag).reset
+      end
+    end
   end
 end
diff --git a/backend/spec/factories/tags.rb b/backend/spec/factories/tags.rb
index 55db316..a9df735 100644
--- a/backend/spec/factories/tags.rb
+++ b/backend/spec/factories/tags.rb
@@ -6,10 +6,15 @@ FactoryBot.define do
 
     category { :general }
     post_count { 0 }
+
     association :tag_name
 
     after(:build) do |tag, evaluator|
       tag.name = evaluator.name if evaluator.name.present?
     end
+
+    after(:create) do |tag|
+      tag.tag_name.update!(tag:) if tag.tag_name.tag_id != tag.id
+    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..d87bb56
--- /dev/null
+++ b/backend/spec/models/locale_spec.rb
@@ -0,0 +1,69 @@
+require 'rails_helper'
+
+RSpec.describe Locale, type: :model do
+  def prepare_french_reference!
+    Language.find_or_create_by!(code: 'fr') { _1.name = 'French' }
+    Script.find_or_create_by!(code: 'Latn') { _1.name = 'Latin' }
+  end
+
+  def create_french_locale!
+    prepare_french_reference!
+    described_class.create!(code: 'fr', language_code: 'fr',
+                            script_code: 'Latn', name: 'French')
+  end
+
+  it 'generates a primary name for every existing tag using the name generator' do
+    first = create(:tag, name: 'first_existing_tag')
+    second = create(:tag, 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, first.name)
+        .and_return('name_from_generator')
+
+    locale = create_french_locale!
+
+    expect(TagName).to have_received(:generate_name).with(locale, first, first.name)
+    expect(TagName).to have_received(:generate_name).with(locale, second, second.name)
+    expect(first.tag_names.find_by!(language_code: 'fr', primary_flg: true))
+        .to have_attributes(name: 'name_from_generator', tag_id: first.id,
+                            language_code: 'fr', script_code: 'Latn',
+                            primary_flg: true, canonical_id: nil)
+    expect(second.tag_names.find_by!(language_code: 'fr', primary_flg: true))
+        .to have_attributes(tag_id: second.id, language_code: 'fr',
+                            script_code: 'Latn', primary_flg: true, canonical_id: nil)
+    expect(TagName.where(language_code: 'fr', 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
+    prepare_french_reference!
+    tag = create(:tag, name: 'already_named')
+    existing = create(:tag_name, name: 'nom_existant', tag:,
+                                 language_code: 'fr', script_code: 'Latn')
+
+    create_french_locale!
+
+    expect(TagName.where(tag_id: tag.id, language_code: 'fr', primary_flg: true))
+        .to contain_exactly(existing)
+    expect(existing.reload).to have_attributes(
+        tag_id: tag.id, language_code: 'fr', script_code: 'Latn', primary_flg: true)
+  end
+
+  it 'creates a primary name when the language has only an alias' do
+    prepare_french_reference!
+    tag = create(:tag, name: 'alias_only_tag')
+    alias_name = create(:tag_name, :alias, name: 'alias_fr',
+                                          canonical: tag.tag_name,
+                                          language_code: 'fr', script_code: 'Latn')
+
+    create_french_locale!
+
+    expect(alias_name.reload).to have_attributes(
+        canonical_id: tag.tag_name_id, tag_id: tag.id,
+        language_code: 'fr', script_code: 'Latn', primary_flg: false)
+    generated = TagName.find_by!(tag_id: tag.id, language_code: 'fr', primary_flg: true)
+    expect(generated).to have_attributes(tag_id: tag.id, language_code: 'fr',
+                                         script_code: 'Latn', primary_flg: true)
+    expect(TagName.where(tag_id: tag.id, language_code: 'fr', primary_flg: true).count).to eq(1)
+  end
+end
diff --git a/backend/spec/models/material_export_item_spec.rb b/backend/spec/models/material_export_item_spec.rb
index d98e225..07e08f3 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, 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_version_spec.rb b/backend/spec/models/post_version_spec.rb
index 4cc0e82..ccbb20f 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, 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/tag_name_sanitisation_rule_spec.rb b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
index b82f9fa..6fb9929 100644
--- a/backend/spec/models/tag_name_sanitisation_rule_spec.rb
+++ b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
@@ -34,9 +34,41 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       described_class.create!(priority: 10, source_pattern: '_', replacement: '')
     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
+        japanese = 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(japanese.reload).to have_attributes(name: 'foobar', language_code: 'ja')
+      end
+
+      it 'renames without merging tags or deleting either language identity' do
+        japanese = create(:tag, name: 'foobar')
+        english_name = create(:tag_name, name: 'temporary',
+                                        language_code: 'en', script_code: 'Latn')
+        english = create(:tag, 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(japanese.reload.tag_name).to have_attributes(
+            name: 'foobar', language_code: 'ja', tag_id: japanese.id)
+        expect(english.reload.tag_name_id).to eq(english_name.id)
+      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
@@ -48,9 +80,9 @@ RSpec.describe TagNameSanitisationRule, type: :model do
     end
 
     context 'when a conflicting canonical tag_name exists' do
-      let!(:existing) { TagName.create!(name: 'foobar') }
+      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
@@ -63,7 +95,7 @@ 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!(:existing) { create(:tag_name, name: 'foobar') }
       let!(:source_tag) { create(:tag, name: 'tmp', category: :general) }
       let!(:source_tag_name_id) { source_tag.tag_name_id }
 
@@ -82,10 +114,10 @@ RSpec.describe TagNameSanitisationRule, type: :model do
     context 'when the sanitised name is an alias of an existing tag' do
       let!(:existing_tag) { create(:tag) }
       let!(:alias_name) do
-        TagName.create!(name: 'foobar', canonical: existing_tag.tag_name)
+        create(:tag_name, :alias, name: 'foobar', canonical: existing_tag.tag_name)
       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
@@ -100,11 +132,11 @@ RSpec.describe TagNameSanitisationRule, type: :model do
     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, 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, tag_name: source_tn, category: :general) }
       let!(:source_tag_name_id) { source_tn.id }
 
       before do
diff --git a/backend/spec/models/tag_name_spec.rb b/backend/spec/models/tag_name_spec.rb
new file mode 100644
index 0000000..66aa120
--- /dev/null
+++ b/backend/spec/models/tag_name_spec.rb
@@ -0,0 +1,73 @@
+require 'rails_helper'
+
+RSpec.describe TagName, type: :model do
+  include_context 'English locale'
+
+  it 'allows the same name in different languages' do
+    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 Japanese 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, tag_id: nil)
+  end
+
+  it 'persists both sides of the representative tag factory association' do
+    tag = create(:tag)
+
+    expect(tag.reload.tag_name.reload.tag_id).to eq(tag.id)
+    expect(tag.tag_name.tag).to eq(tag)
+  end
+
+  it 'accepts an alias owned by the canonical tag' do
+    tag = create(:tag)
+    alias_name = build(:tag_name, name: 'valid_alias', canonical: tag.tag_name,
+                                 tag:, primary_flg: false)
+
+    expect(alias_name).to have_attributes(
+        canonical_id: tag.tag_name_id, tag_id: tag.id,
+        primary_flg: false, language_code: 'ja')
+    expect(alias_name).to be_valid
+  end
+
+  describe '.canonicalise' do
+    it 'resolves only aliases in the requested language' do
+      japanese = create(:tag, name: 'japanese_canonical')
+      english_name = create(:tag_name, name: 'english_canonical',
+                                      language_code: 'en', script_code: 'Latn')
+      english = create(:tag, tag_name: english_name)
+      japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                 canonical: japanese.tag_name)
+      english_alias = create(:tag_name, :alias, name: 'temporary_alias',
+                                                canonical: english_name,
+                                                language_code: 'en', script_code: 'Latn')
+      english_alias.update_columns(name: 'shared_alias')
+
+      expect(japanese_alias.reload).to have_attributes(
+          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          primary_flg: false, language_code: 'ja')
+      expect(english_alias.reload).to have_attributes(
+          canonical_id: english_name.id, 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(['japanese_canonical'])
+    end
+  end
+end
diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index d63be45..e9683dd 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -9,7 +9,7 @@ RSpec.describe Tag, type: :model do
         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
@@ -25,19 +25,49 @@ RSpec.describe Tag, type: :model do
   end
 
   describe '.normalise_tags!' do
+    it 'canonicalises aliases in the supplied language only' do
+      Language.find_or_create_by!(code: 'en') { _1.name = 'English' }
+      Script.find_or_create_by!(code: 'Latn') { _1.name = 'Latin' }
+      Locale.insert_all!([
+          { code: 'en', language_code: 'en', script_code: 'Latn',
+            name: 'English', created_at: Time.current }]) unless Locale.exists?(code: 'en')
+      english_locale = Locale.find('en')
+      japanese = create(:tag, name: 'japanese_canonical')
+      english_name = create(:tag_name, name: 'english_canonical',
+                                      language_code: 'en', script_code: 'Latn')
+      english = create(:tag, tag_name: english_name)
+      japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                 canonical: japanese.tag_name)
+      english_alias = create(:tag_name, :alias, name: 'temporary_alias',
+                                                canonical: english_name,
+                                                language_code: 'en', script_code: 'Latn')
+      english_alias.update_columns(name: 'shared_alias')
+
+      expect(japanese_alias.reload).to have_attributes(
+          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          primary_flg: false, language_code: 'ja')
+      expect(english_alias.reload).to have_attributes(
+          canonical_id: english_name.id, 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([japanese])
+    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,
+          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,
+            [deprecated_tag.name],
+            deny_deprecated: true)
       }.to raise_error(Tag::DeprecatedTagNormalisationError) { |error|
         expect(error.tag_names).to eq([deprecated_tag.name])
       }
@@ -45,88 +75,79 @@ RSpec.describe Tag, type: :model do
 
     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' }
       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' }
       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' }
       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' }
       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' }
       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' }
       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' }
       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' }
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
@@ -183,11 +204,65 @@ 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
+        tag = described_class.find_or_create_by_tag_name!(
+            locale, 'english_name', category: :character)
+
+        expect(tag.tag_name.reload).to have_attributes(
+            language_code: 'en', script_code: 'Latn',
+            primary_flg: true, tag_id: tag.id)
+        expect(tag.category).to eq('character')
+      end
+
+      it 'creates separate tag identities for the same name in different languages' do
+        japanese = 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(japanese)
+        expect(english.tag_name.language_code).to eq('en')
+        expect(japanese.tag_name.language_code).to eq('ja')
+        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(japanese)
+      end
+
+      it 'preserves the V1 representative when looking up another primary language' do
+        tag = create(:tag, name: '日本語代表名')
+        representative_id = tag.tag_name_id
+        english = create(:tag_name, name: 'english_primary', tag:,
+            language_code: 'en', script_code: 'Latn')
+
+        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
+        tags = described_class.normalise_tags!(
+            locale, ['character:normalised_english'],
+            with_tagme: false, with_no_deerjikist: false)
+
+        expect(tags.length).to eq(1)
+        expect(tags.first.tag_name).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)
 
@@ -197,27 +272,38 @@ RSpec.describe Tag, type: :model do
 
     it 'reuses the canonical 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', canonical: tag.tag_name)
+      expect(alias_name.reload).to have_attributes(
+          canonical_id: tag.tag_name_id, 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 canonical tag through another alias' do
+      tag = create(:tag)
+      canonical = tag.tag_name
+      alias_name = create(:tag_name, :alias, name: 'lookup_alias', canonical:)
+      other_alias = create(:tag_name, :alias, name: 'lookup_other_alias', canonical:)
+
+      expect([alias_name.reload, other_alias.reload]).to all(have_attributes(
+          canonical_id: canonical.id, 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)
     end
@@ -277,7 +363,7 @@ RSpec.describe Tag, type: :model do
     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_alias = create(:tag_name, :alias, name: 'merge_alias', canonical: source_tag_name)
       TagVersioning.ensure_snapshot!(source_tag, created_by_user: user)
       original_version = source_tag.tag_versions.first
 
diff --git a/backend/spec/requests/gekanator_learning_spec.rb b/backend/spec/requests/gekanator_learning_spec.rb
index 26f271b..855bb75 100644
--- a/backend/spec/requests/gekanator_learning_spec.rb
+++ b/backend/spec/requests/gekanator_learning_spec.rb
@@ -898,12 +898,11 @@ 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, name: 'active_question_tag', category: :general)
+      deprecated_tag = create(:tag,
+          name: 'deprecated_question_tag',
+          category: :general,
+          deprecated_at: Time.current)
 
       [active_tag, deprecated_tag].each do |question_tag|
         GekanatorQuestion.create!(
diff --git a/backend/spec/requests/gekanator_posts_spec.rb b/backend/spec/requests/gekanator_posts_spec.rb
index b21e414..7fe627a 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, name: 'active tag', category: :general)
+      deprecated_tag = create(:tag,
+          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..f90a8c3
--- /dev/null
+++ b/backend/spec/requests/locale_write_paths_spec.rb
@@ -0,0 +1,232 @@
+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
+    expect(tag_name.tag.tag_name_id).to eq(tag_name.id)
+    tag_name.tag
+  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 Japanese fallback' do
+        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 Japanese fallback' do
+        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
+        # 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
+        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
+        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
+        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
+        tag = create(:tag)
+
+        put "/tags/#{ tag.id }", params: locale_params.merge(
+            name: tag.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, tag_name: english_name, category: :material) }
+    let!(:japanese_tag) do
+      create(:tag, name: 'temporary_japanese', category: :general).tap do |tag|
+        # Isolate lookup from the separately tested uniqueness validation.
+        tag.tag_name.update_columns(name: 'shared_name')
+      end
+    end
+
+    it 'plans and creates the post using the English identity and category' do
+      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(japanese_tag)
+      expect(english_tag.reload.category).to eq('material')
+      expect(japanese_tag.reload.category).to eq('general')
+    end
+
+    it 'updates the post using the English identity' do
+      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(japanese_tag)
+    end
+
+    it 'resolves the English material tag' do
+      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: japanese_tag)).to be_empty
+    end
+
+    it 'resolves the English parent tag' do
+      child = create(:tag)
+
+      put "/tags/#{ child.id }", params: {
+          locale: 'en', name: child.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
+      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, tag_name: english_name) }
+
+    it 'allows a rename to a name already used in Japanese' do
+      japanese = create(:tag, name: 'rename_target')
+
+      patch "/tags/#{ tag.id }", params: { locale: 'en', name: 'rename_target' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(tag.reload.tag_name).to have_attributes(
+          name: 'rename_target', language_code: 'en', tag_id: tag.id)
+      expect(japanese.reload.tag_name).to have_attributes(
+          name: 'rename_target', language_code: 'ja', tag_id: japanese.id)
+    end
+
+    it 'creates aliases in the requested language' do
+      put "/tags/#{ tag.id }", params: {
+          locale: 'en', name: tag.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', canonical_id: english_name.id,
+              tag_id: tag.id, primary_flg: false, language_code: 'en')
+      expect(tag.reload.tag_name_id).to eq(english_name.id)
+    end
+
+    it 'does not take an alias from another language' do
+      japanese = create(:tag, name: 'japanese_owner')
+      japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                canonical: japanese.tag_name)
+      expect(japanese_alias.reload).to have_attributes(
+          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          primary_flg: false, language_code: 'ja')
+
+      put "/tags/#{ tag.id }", params: {
+          locale: 'en', name: tag.name, category: tag.category, deprecated: false,
+          aliases: 'shared_alias', parent_tags: '' }
+
+      expect(response).to have_http_status(:ok), response.body
+      expect(japanese_alias.reload).to have_attributes(
+          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          primary_flg: false, language_code: 'ja')
+      expect(TagName.find_by!(language_code: 'en', name: 'shared_alias'))
+          .to have_attributes(
+              canonical_id: english_name.id, tag_id: tag.id,
+              primary_flg: false, language_code: 'en')
+    end
+  end
+end
diff --git a/backend/spec/requests/materials_spec.rb b/backend/spec/requests/materials_spec.rb
index c1ffdf4..17ff0a9 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, 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, 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, name: 'material_scope_root',
                       category: :material)
       child_b =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_b'),
+          create(:tag, name: 'material_scope_b',
                       category: :material)
       child_a =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_a'),
+          create(:tag, name: 'material_scope_a',
                       category: :material)
       deprecated =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_old'),
+          create(:tag, name: 'material_scope_old',
                       category: :material,
                       deprecated_at: Time.current)
       grandchild =
-          Tag.create!(tag_name: TagName.create!(name: 'material_scope_grandchild'),
+          create(:tag, 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, name: 'material_show', category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'show.png'))
@@ -323,8 +323,8 @@ 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, tag_name: general_tag_name, category: :general)
 
         post '/materials', params: {
           tag: 'material_create_general_tag',
@@ -384,7 +384,7 @@ 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, name: 'material_update_old', category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'old.png'))
@@ -508,7 +508,7 @@ 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, name: 'material_update_existing_no_history',
                         category: :material)
 
         expect(existing_tag.tag_versions).to be_empty
@@ -531,7 +531,7 @@ 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, name: 'material_update_character_no_history',
                         category: :character)
 
         expect(existing_tag.tag_versions).to be_empty
@@ -651,8 +651,8 @@ 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, name: 'zip_a', category: :material) }
+    let!(:tag_b) { create(:tag, 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 +701,7 @@ 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, name: 'material_history', category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'history.png'))
@@ -776,7 +776,7 @@ 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, 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..f800afb 100644
--- a/backend/spec/requests/nico_tags_spec.rb
+++ b/backend/spec/requests/nico_tags_spec.rb
@@ -162,11 +162,11 @@ 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, 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, tag_name: linked_b_name, category: :general)
 
       NicoTagVersionRecorder.record!(external_tag: nico_tag,
                                      event_type: :create, created_by_user: admin)
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 8660634..585dacb 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, 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, tag_name:, category: :general) }
+    let!(:tag_name2) { create(:tag_name, name: 'unko') }
+    let!(:tag2) { create(:tag, tag_name: tag_name2, category: :deerjikist) }
+    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', canonical: tag_name) }
 
     let!(:hit_post) do
       Post.create!(uploaded_user: user, title: 'hello spec world',
@@ -341,17 +341,17 @@ 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, 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, 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, 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', canonical: foo_tag_name)
       end
 
       let!(:foo_only_post) do
@@ -772,11 +772,10 @@ 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,
+            name: 'deprecated_post_tag',
+            category: :general,
+            deprecated_at: Time.current)
         PostTag.create!(post: post_record, tag: deprecated_tag)
 
         request
@@ -853,9 +852,9 @@ 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, tag_name:, category: :general)
+              create(:tag_name, :alias, name: "show_query_alias_#{ i }", canonical: tag_name)
               PostTag.create!(post: post_record, tag:)
               tag
             end
@@ -1000,7 +999,7 @@ 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', canonical: tag_name) }
 
     it '401 when not logged in' do
       sign_out
@@ -1157,11 +1156,10 @@ 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,
+          name: 'deprecated_direct_tag',
+          category: :general,
+          deprecated_at: Time.current)
       sign_in_as(member)
 
       post '/posts', params: post_write_params(
@@ -1178,18 +1176,16 @@ 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, name: 'active_child', category: :general)
+      deprecated_parent = create(:tag,
+          name: 'deprecated_parent',
+          category: :general,
+          deprecated_at: Time.current)
+      deprecated_grandparent = create(:tag,
+          name: 'deprecated_grandparent',
+          category: :general,
+          deprecated_at: Time.current)
+      active_grandparent = create(:tag, 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)
@@ -1622,6 +1618,7 @@ 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 +1655,8 @@ 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, tag_name: tn2, category: :general)
 
       put "/posts/#{post_record.id}", params: post_update_params(
           post_record,
@@ -1707,11 +1704,10 @@ 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,
+          name: 'deprecated_update_tag',
+          category: :general,
+          deprecated_at: Time.current)
       sign_in_as(member)
 
       put "/posts/#{ post_record.id }", params: post_update_params(
@@ -1986,7 +1982,8 @@ 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!(
@@ -2015,7 +2012,8 @@ 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!(
@@ -2102,7 +2100,8 @@ 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)
@@ -2191,8 +2190,8 @@ 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, tag_name: tag_name2, category: :general) }
 
     def snapshot_tags(post)
       post.snapshot_tag_names.join(' ')
@@ -2550,8 +2549,8 @@ 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, tag_name: tag_name2, category: :general)
 
       expect do
         put "/posts/#{post_record.id}", params: post_write_params(
@@ -2715,8 +2714,8 @@ 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, 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..f9802a4 100644
--- a/backend/spec/requests/tag_versions_spec.rb
+++ b/backend/spec/requests/tag_versions_spec.rb
@@ -232,8 +232,8 @@ 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, 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..33401e9 100644
--- a/backend/spec/requests/tag_wiki_history_integrity_spec.rb
+++ b/backend/spec/requests/tag_wiki_history_integrity_spec.rb
@@ -8,8 +8,8 @@ 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, tag_name:, category:)
   end
 
   def create_wiki_for_tag! tag:, body: 'wiki body', user: member_user
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index 3c1088c..26c1b52 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, tag_name: tn, category: :general) }
+  let!(:alias_tn) { create(:tag_name, :alias, name: 'unko', canonical: tn) }
   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, tag_name: tn2, category: :general) }
 
   def response_tags
     json.fetch('tags')
@@ -91,7 +91,7 @@ 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, name: 'meme_only', category: :meme)
 
       get '/tags', params: { category: 'meme' }
 
@@ -101,12 +101,11 @@ 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,
+          name: 'deprecated_filter',
+          category: :general,
+          deprecated_at: 1.day.from_now)
+      active_tag = create(:tag, name: 'active_filter', category: :general)
 
       get '/tags', params: { name: '_filter', deprecated: '1' }
 
@@ -122,9 +121,9 @@ RSpec.describe 'Tags API', type: :request do
     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, name: 'pc_low', category: :general)
+      mid = create(:tag, name: 'pc_mid', category: :general)
+      high = create(:tag, name: 'pc_high', category: :general)
 
       low.update_columns(post_count: 1)
       mid.update_columns(post_count: 3)
@@ -142,8 +141,8 @@ 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, name: 'created_old', category: :general)
+      new_tag = create(:tag, 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 +161,8 @@ 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, name: 'updated_old', category: :general)
+      new_tag = create(:tag, 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 +181,12 @@ 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, name: 'cat_deerjikist', category: :deerjikist)
+      create(:tag, name: 'cat_meme', category: :meme)
+      create(:tag, name: 'cat_character', category: :character)
+      create(:tag, name: 'cat_general', category: :general)
+      create(:tag, name: 'cat_material', category: :material)
+      create(:tag, name: 'cat_meta', category: :meta)
       create(:external_tag, name: 'cat_nico')
 
       get '/tags', params: { name: 'cat_', order: 'category:asc', limit: 20 }
@@ -202,20 +201,20 @@ 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)
+            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)
+            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)
+            tag_name: create(:tag_name, name: 'z_mixed_page'),
+            category: :general)
       end
 
       let!(:first_external) do
@@ -265,7 +264,7 @@ 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, tag_name: create(:tag_name, name:), category: :general)
       end
 
       get '/tags', params: { name: 'pag_', order: 'name:asc', page: 2, limit: 2 }
@@ -276,8 +275,8 @@ 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, name: 'fallback_low', category: :general)
+      high = create(:tag, name: 'fallback_high', category: :general)
 
       low.update_columns(post_count: 1)
       high.update_columns(post_count: 9)
@@ -290,7 +289,7 @@ 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, tag_name: create(:tag_name, name:), category: :general)
       end
 
       get '/tags', params: { name: 'norm_', order: 'name:asc', page: 0, limit: 0 }
@@ -302,10 +301,9 @@ 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,
+          tag_name: create(:tag_name, name: 'index_parent_tag'),
+          category: :meme)
       TagImplication.create!(tag:, parent_tag:)
 
       get '/tags', params: { name: 'spec_tag' }
@@ -349,10 +347,9 @@ 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,
+            tag_name: create(:tag_name, name: 'show_parent_tag'),
+            category: :character)
         TagImplication.create!(tag:, parent_tag:)
 
         request
@@ -416,7 +413,7 @@ 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, name: 'mixed_internal', post_count: 2)
       external = create(:external_tag, id: internal.id,
                                        name: 'mixed_external', post_count: 3)
 
@@ -455,7 +452,7 @@ 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, name:, post_count: 1)
         create(:external_tag, name:, post_count: 1)
       end
 
@@ -467,9 +464,9 @@ 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, name: 'switch_internal', post_count: 1)
+      alias_target = create(:tag, category: :general, name: 'alias_target', post_count: 1)
+      create(:tag_name, :alias, name: 'switch_alias', canonical: alias_target.tag_name)
       create(:external_tag, name: 'switch_external', post_count: 1)
 
       get '/tags/autocomplete', params: { q: 'switch', nico: '0' }
@@ -484,11 +481,13 @@ RSpec.describe 'Tags API', type: :request do
     ['%', '_'].each do |wildcard|
       it "treats #{ wildcard } literally for canonical, 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, name: literal, post_count: 1)
+        alias_target = create(
+            :tag, category: :general, name: 'literal_alias_target', post_count: 1)
+        create(:tag_name, :alias, name: "#{ literal }_alias",
+                                  canonical: alias_target.tag_name)
         create(:external_tag, name: literal, post_count: 1)
-        Tag.create!(category: :general, name: 'literalXmatch', post_count: 2)
+        create(:tag, category: :general, name: 'literalXmatch', post_count: 2)
         create(:external_tag, name: 'literalXmatch', post_count: 2)
 
         get '/tags/autocomplete', params: { q: "literal#{ wildcard }" }
@@ -523,11 +522,10 @@ 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,
+          name: 'spec_deprecated',
+          category: :general,
+          deprecated_at: Time.current)
       deprecated_tag.update_columns(post_count: 1)
 
       get '/tags/autocomplete', params: { q: 'spec_', present: '0' }
@@ -820,27 +818,27 @@ RSpec.describe 'Tags API', type: :request do
 
   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, 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, 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, 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, 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, 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, name: 'depth_child_general', category: :general)
     end
 
     before do
@@ -883,15 +881,13 @@ 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,
+          name: 'depth_deprecated_middle',
+          category: :character,
+          deprecated_at: Time.current)
+      visible_descendant = create(:tag,
+          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 +899,20 @@ 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,
+          name: 'depth_active_child_below_deprecated',
+          category: :character)
+      deprecated_parent = create(:tag,
+          name: 'depth_deprecated_parent',
+          category: :character,
+          deprecated_at: Time.current)
+      deprecated_grandparent = create(:tag,
+          name: 'depth_deprecated_grandparent',
+          category: :material,
+          deprecated_at: Time.current)
+      active_ancestor = create(:tag,
+          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 +937,13 @@ 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,
+          name: 'depth_root_below_deprecated',
+          category: :character)
+      deprecated_parent = create(:tag,
+          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 +957,14 @@ 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,
+          name: 'depth_cycle_first',
+          category: :character,
+          deprecated_at: Time.current)
+      second = create(:tag,
+          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 +990,19 @@ 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, 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, 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, name: 'materials_child_b', category: :character)
     end
 
     let!(:grandchild_tag) do
-      Tag.create!(tag_name: TagName.create!(name: 'materials_grandchild'), category: :material)
+      create(:tag, name: 'materials_grandchild', category: :material)
     end
 
     let!(:root_material) do
@@ -1158,14 +1146,12 @@ 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,
+            tag_name: create(:tag_name, name: 'put_old_parent'),
+            category: :general)
+        kept_parent = create(:tag,
+            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)
 
@@ -1310,14 +1296,12 @@ RSpec.describe 'Tags API', type: :request do
       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,
+            tag_name: create(:tag_name, name: 'put_snapshot_old_parent'),
+            category: :general)
+        new_parent = create(:tag,
+            tag_name: create(:tag_name, name: 'put_snapshot_new_parent'),
+            category: :general)
         TagImplication.create!(tag:, parent_tag: old_parent)
 
         put "/tags/#{ tag.id }", params: {
@@ -1454,14 +1438,12 @@ 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,
+            tag_name: create(:tag_name, name: 'put_alias_old_owner'),
+            category: :general)
+        stolen_alias = create(:tag_name, :alias,
+            name: 'put_stolen_alias',
+            canonical: old_owner.tag_name)
 
         expect(old_owner.tag_name.aliases.map(&:name)).to include('put_stolen_alias')
 
@@ -1492,14 +1474,12 @@ RSpec.describe 'Tags API', type: :request do
       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,
+            tag_name: create(:tag_name, name: 'put_alias_collision_owner'),
+            category: :general)
+        stolen_alias = create(:tag_name, :alias,
+            name: 'put_alias_collision_name',
+            canonical: old_owner.tag_name)
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: tag.tag_name,
@@ -1515,7 +1495,7 @@ 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
@@ -1534,10 +1514,9 @@ RSpec.describe 'Tags API', type: :request do
       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,
+            tag_name: create(:tag_name, name: 'put_cycle_child'),
+            category: :general)
 
         TagImplication.create!(tag: child, parent_tag: tag)
 
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..7bf7c49 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,
+        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, 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, tag_name: linked_tag_name, category: :general)
 
     linked_page =
         Wiki::Commit.create_content!(
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..7d34dc6 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, 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..b7811c4 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, 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..9cd5d7b 100644
--- a/backend/spec/services/post_bulk_creator_spec.rb
+++ b/backend/spec/services/post_bulk_creator_spec.rb
@@ -1,6 +1,8 @@
 require 'rails_helper'
 
 RSpec.describe PostBulkCreator do
+  include_context 'English locale'
+
   it 'limits workers to two and keeps failures in their request slots' do
     actor = instance_double(User, id: 123)
     allow(User).to receive(:find).with(123) {
@@ -9,6 +11,7 @@ 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 +31,7 @@ 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 +49,12 @@ 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)
diff --git a/backend/spec/services/post_create_plan_spec.rb b/backend/spec/services/post_create_plan_spec.rb
index 71a19c1..e87b492 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, name:, category:)
   end
 
   before do
@@ -10,6 +10,56 @@ 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
+      english_name = create(:tag_name, name: 'shared_name',
+                                      language_code: 'en', script_code: 'Latn')
+      english = create(:tag, tag_name: english_name, category: :character)
+      japanese = create(:tag, name: 'temporary_japanese', category: :general)
+      # The DB permits this identity; validation has its own contract spec.
+      japanese.tag_name.update_columns(name: 'shared_name')
+      english_parent = create(:tag, name: 'english_parent', category: :material)
+      japanese_parent = create(:tag, name: 'japanese_parent', category: :general)
+      TagImplication.create!(tag: english, parent_tag: english_parent)
+      TagImplication.create!(tag: japanese, parent_tag: japanese_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: english_parent.name, category: :material })
+      expect(plan[:post_tag_specs].pluck(:name)).not_to include(japanese_parent.name)
+    end
+
+    it 'resolves aliases within the requested language' do
+      japanese = create(:tag, name: 'japanese_canonical')
+      english_name = create(:tag_name, name: 'english_canonical',
+                                      language_code: 'en', script_code: 'Latn')
+      english = create(:tag, tag_name: english_name, category: :character)
+      japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                canonical: japanese.tag_name)
+      english_alias = create(:tag_name, :alias, name: 'temporary_alias',
+                                               canonical: english_name,
+                                               language_code: 'en', script_code: 'Latn')
+      english_alias.update_columns(name: 'shared_alias')
+
+      expect(japanese_alias.reload).to have_attributes(
+          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          primary_flg: false, language_code: 'ja')
+      expect(english_alias.reload).to have_attributes(
+          canonical_id: english_name.id, 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, category: :character }])
+    end
+  end
+
   it 'plans direct and existing default tags without persisting records' do
     counts = [TagName.count, Tag.count]
 
@@ -18,7 +68,7 @@ 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(
@@ -31,7 +81,7 @@ RSpec.describe PostCreatePlan do
 
   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)
+    create(:tag_name, :alias, name: 'にじか', canonical: canonical.tag_name)
     create_tag!('動画', :meta)
 
     plan = described_class.new(
@@ -40,7 +90,7 @@ 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 +105,7 @@ 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 +123,7 @@ 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 +137,7 @@ 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..2fa36cc 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 +71,34 @@ 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
+        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..5bc7bcc 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, 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/wiki/commit_integrity_spec.rb b/backend/spec/services/wiki/commit_integrity_spec.rb
index 4a08de5..9351d75 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, 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..5d82b34 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, 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, 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..fa873ef
--- /dev/null
+++ b/backend/spec/support/locale_context.rb
@@ -0,0 +1,13 @@
+RSpec.shared_context 'English locale' do
+  let!(:locale) do
+    Language.find_or_create_by!(code: 'en') { _1.name = 'English' }
+    Script.find_or_create_by!(code: 'Latn') { _1.name = 'Latin' }
+    unless Locale.exists?(code: 'en')
+      # Reference data only: do not generate names for unrelated existing tags.
+      Locale.insert_all!([
+          { code: 'en', language_code: 'en', script_code: 'Latn',
+            name: 'English', created_at: Time.current }])
+    end
+    Locale.find('en')
+  end
+end
diff --git a/backend/spec/tasks/nico_sync_spec.rb b/backend/spec/tasks/nico_sync_spec.rb
index b3c053f..e62a8f3 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)
diff --git a/backend/spec/tasks/post_similarity_calc_spec.rb b/backend/spec/tasks/post_similarity_calc_spec.rb
index 20dd575..1934f66 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, name: 't1')
+    t2 = create(:tag, name: 't2')
+    t3 = create(:tag, name: 't3')
+    deprecated_tag = create(:tag, 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..fe293a6 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, name: 't1')
+    t2 = create(:tag, name: 't2')
+    t3 = create(:tag, name: 't3')
+    deprecated_tag = create(:tag, name: 'deprecated', deprecated_at: Time.current)
 
     p1 = Post.create!(url: "https://example.com/1")
     p2 = Post.create!(url: "https://example.com/2")