FEATURE: Show translated category names from localizations table if they exist for the user locale (#32380)

This PR adds category localization support to core.

- Depends on https://github.com/discourse/discourse/pull/32378
- Creates the required table `category_localizations`
- Makes use of the site category cache to display localized categories
- Supports name and description
- This does not yet include /categories page. (coming in a next PR)

## Before

<img width="1089" alt="Screenshot 2025-04-21 at 4 31 43 PM"
src="https://github.com/user-attachments/assets/9e49b21b-b16a-43d2-9b16-0fd0324a21ca"
/>

## After

<img width="1085" alt="Screenshot 2025-04-21 at 4 32 42 PM"
src="https://github.com/user-attachments/assets/7bfa21a2-6df2-4cdf-a00a-d044c3526a40"
/>

app/models/category.rb

@@ -36,6 +36,7 @@ class Category < ActiveRecord::Base
   has_many :category_users
   has_many :category_featured_topics
   has_many :featured_topics, through: :category_featured_topics, source: :topic
+  has_many :category_localizations, dependent: :destroy
 
   has_many :category_groups, dependent: :destroy
   has_many :category_moderation_groups, dependent: :destroy

app/models/category_localization.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+class CategoryLocalization < ActiveRecord::Base
+  belongs_to :category
+
+  validates :locale, presence: true, length: { maximum: 20 }
+  validates :name, presence: true, length: { maximum: 50 }
+  validates :category_id, uniqueness: { scope: :locale }
+
+  after_commit :invalidate_site_cache
+
+  def invalidate_site_cache
+    I18n.with_locale(locale) { Site.clear_cache }
+  end
+end
+
+# == Schema Information
+#
+# Table name: category_localizations
+#
+#  id          :bigint           not null, primary key
+#  category_id :bigint           not null
+#  locale      :string(20)       not null
+#  name        :string(50)       not null
+#  description :text
+#  created_at  :datetime         not null
+#  updated_at  :datetime         not null
+#
+# Indexes
+#
+#  index_category_localizations_on_category_id             (category_id)
+#  index_category_localizations_on_category_id_and_locale  (category_id,locale) UNIQUE
+#

app/models/site.rb

@@ -73,24 +73,35 @@ class Site
         categories =
           begin
             query =
-              Category
-                .includes(
-                  :uploaded_logo,
-                  :uploaded_logo_dark,
-                  :uploaded_background,
-                  :uploaded_background_dark,
-                  :tags,
-                  :tag_groups,
-                  :form_templates,
-                  category_required_tag_groups: :tag_group,
-                )
-                .joins("LEFT JOIN topics t on t.id = categories.topic_id")
-                .select("categories.*, t.slug topic_slug")
-                .order(:position)
+              Category.includes(
+                :uploaded_logo,
+                :uploaded_logo_dark,
+                :uploaded_background,
+                :uploaded_background_dark,
+                :tags,
+                :tag_groups,
+                :form_templates,
+                category_required_tag_groups: :tag_group,
+              ).joins("LEFT JOIN topics t on t.id = categories.topic_id")
 
+            if SiteSetting.experimental_content_localization
+              locale = I18n.locale.to_s
+              query =
+                query.joins(
+                  "LEFT JOIN category_localizations cl ON cl.category_id = categories.id AND cl.locale = '#{ActiveRecord::Base.connection.quote_string(locale)}'",
+                ).select(
+                  "categories.*,
+                      t.slug topic_slug,
+                      COALESCE(cl.name, categories.name) AS name,
+                      COALESCE(cl.description, categories.description) AS description",
+                )
+            else
+              query = query.select("categories.*, t.slug topic_slug")
+            end
+
+            query = query.order(:position)
             query =
               DiscoursePluginRegistry.apply_modifier(:site_all_categories_cache_query, query, self)
-
             query.to_a
           end
 

config/locales/server.en.yml

@@ -2768,6 +2768,7 @@ en:
     about_page_hidden_groups: "Do not show members of specific groups on the /about page."
     adobe_analytics_tags_url: "Adobe Analytics tags URL (`https://assets.adobedtm.com/...`)"
     view_raw_email_allowed_groups: "Groups which can view the raw email content of a post if it was created by an incoming email. This includes email headers and other technical information."
+    experimental_content_localization: "Displays localized content for users based on their language preferences. Such content may include categories, tags, posts, and topics. This feature is under heavy development."
     errors:
       invalid_css_color: "Invalid color. Enter a color name or hex value."
       invalid_email: "Invalid email address."

config/site_settings.yml

@@ -3973,3 +3973,6 @@ experimental:
     client: true
     default: false
     hidden: true
+  experimental_content_localization:
+    client: true
+    default: false

db/migrate/20250421074012_create_category_localization_table.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class CreateCategoryLocalizationTable < ActiveRecord::Migration[7.2]
+  def change
+    create_table :category_localizations do |t|
+      t.references :category, null: false
+      t.string :locale, limit: 20, null: false
+      t.string :name, limit: 50, null: false
+      t.text :description, null: true
+
+      t.timestamps null: false
+    end
+
+    add_index :category_localizations, %i[category_id locale], unique: true
+  end
+end

spec/fabricators/category_localization_fabricator.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+Fabricator(:category_localization) do
+  category
+  locale "ja"
+  name { sequence(:name) { |i| "ワク" * (i + 1) } }
+  description "日本のディスカッション"
+end

spec/models/category_localization_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+describe CategoryLocalization do
+  context "when commit" do
+    it "clears the site cache for the locale" do
+      category = Fabricate(:category, name: "yy")
+
+      I18n.locale = "es"
+      expect(Site.all_categories_cache.pluck(:name)).to include("yy")
+
+      I18n.locale = "en"
+      expect(Site.all_categories_cache.pluck(:name)).to include("yy")
+
+      category.update_columns(name: "zz")
+
+      I18n.locale = "es"
+      expect(Site.all_categories_cache.pluck(:name)).to include("yy")
+      I18n.locale = "en"
+      expect(Site.all_categories_cache.pluck(:name)).to include("yy")
+
+      Fabricate(:category_localization, name: "Japón", locale: "es", category:)
+
+      I18n.locale = "es"
+      expect(Site.all_categories_cache.pluck(:name)).to include("zz")
+      I18n.locale = "en"
+      expect(Site.all_categories_cache.pluck(:name)).to include("yy")
+    end
+  end
+end

spec/models/site_spec.rb

@@ -344,5 +344,33 @@ RSpec.describe Site do
         &modifier_block
       )
     end
+
+    describe "experimental_content_localization" do
+      it "returns localized category names when enabled" do
+        SiteSetting.experimental_content_localization = true
+
+        localization = Fabricate(:category_localization)
+        category = localization.category
+        locale = localization.locale.to_sym
+
+        I18n.locale = locale
+
+        all_categories_cache = Site.all_categories_cache
+        cached_category = all_categories_cache.find { |c| c[:id] == category.id }
+        expect(cached_category[:name]).to eq(localization.name)
+        expect(cached_category[:description]).to eq(localization.description)
+      end
+
+      it "returns original names when enabled" do
+        SiteSetting.experimental_content_localization = true
+
+        category = Fabricate(:category, name: "derp", description: "derp derp")
+
+        all_categories_cache = Site.all_categories_cache
+        cached_category = all_categories_cache.find { |c| c[:id] == category.id }
+        expect(cached_category[:name]).to eq(category.name)
+        expect(cached_category[:description]).to eq(category.description)
+      end
+    end
   end
 end