FEATURE: new site setting to set locale from cookie for anonymous users. (#18377)

This new hidden default-disabled site setting `set_locale_from_cookie` will set locale from anonymous user's cookie value.

app/controllers/application_controller.rb

@@ -400,11 +400,8 @@ class ApplicationController < ActionController::Base
     if check_current_user && (user = current_user rescue nil)
       locale = user.effective_locale
     else
-      if SiteSetting.set_locale_from_accept_language_header
+      locale = Discourse.anonymous_locale(request)
-        locale = locale_from_header
+      locale ||= SiteSetting.default_locale
-      else
-        locale = SiteSetting.default_locale
-      end
     end
 
     if !I18n.locale_available?(locale)
@@ -624,10 +621,6 @@ class ApplicationController < ActionController::Base
 
   private
 
-  def locale_from_header
-    HttpLanguageParser.parse(request.env["HTTP_ACCEPT_LANGUAGE"])
-  end
-
   def preload_anonymous_data
     store_preloaded("site", Site.json_for(guardian))
     store_preloaded("siteSettings", SiteSetting.client_settings_json)

config/site_settings.yml

@@ -123,6 +123,11 @@ basic:
     default: false
     client: true
     validator: "AllowUserLocaleEnabledValidator"
+  set_locale_from_cookie:
+    default: false
+    hidden: true
+    client: true
+    validator: "AllowUserLocaleEnabledValidator"
   support_mixed_text_direction:
     client: true
     default: false

lib/discourse.rb

@@ -1085,4 +1085,10 @@ module Discourse
     Theme.all.each(&:update_javascript_cache!)
     Theme.expire_site_cache!
   end
+
+  def self.anonymous_locale(request)
+    locale = HttpLanguageParser.parse(request.cookies["locale"]) if SiteSetting.set_locale_from_cookie
+    locale ||= HttpLanguageParser.parse(request.env["HTTP_ACCEPT_LANGUAGE"]) if SiteSetting.set_locale_from_accept_language_header
+    locale
+  end
 end

lib/middleware/anonymous_cache.rb

@@ -100,8 +100,8 @@ module Middleware
       end
 
       def key_locale
-        if SiteSetting.set_locale_from_accept_language_header
+        if locale = Discourse.anonymous_locale(@request)
-          HttpLanguageParser.parse(@env["HTTP_ACCEPT_LANGUAGE"])
+          locale
         else
           "" # No need to key, it is the same for all anon users
         end

spec/lib/middleware/anonymous_cache_spec.rb

@@ -53,7 +53,7 @@ RSpec.describe Middleware::AnonymousCache do
       end
     end
 
-    context "with header-based locale locale" do
+    context "with header or cookie based custom locale" do
       it "handles different languages" do
         # Normally does not check the language header
         french1 = new_helper("HTTP_ACCEPT_LANGUAGE" => "fr").cache_key
@@ -76,6 +76,9 @@ RSpec.describe Middleware::AnonymousCache do
         expect(none).to eq(english)
         expect(french1).to eq(french2)
         expect(french1).not_to eq(none)
+
+        SiteSetting.set_locale_from_cookie = true
+        expect(new_helper("HTTP_COOKIE" => "locale=es;").cache_key).to include("l=es")
       end
     end
 

spec/requests/application_controller_spec.rb

@@ -895,6 +895,44 @@ RSpec.describe ApplicationController do
         end
       end
     end
+
+    context "with set_locale_from_cookie enabled" do
+      context "when cookie locale differs from default locale" do
+        before do
+          SiteSetting.allow_user_locale = true
+          SiteSetting.set_locale_from_cookie = true
+          SiteSetting.default_locale = "en"
+        end
+
+        context "with an anonymous user" do
+          it "uses the locale from the cookie" do
+            get "/bootstrap.json", headers: { Cookie: "locale=es" }
+            expect(response.status).to eq(200)
+            expect(response.parsed_body['bootstrap']['locale_script']).to end_with("es.js")
+            expect(I18n.locale.to_s).to eq(SiteSettings::DefaultsProvider::DEFAULT_LOCALE) # doesn't leak after requests
+          end
+        end
+
+        context "when the preferred locale includes a region" do
+          it "returns the locale and region separated by an underscore" do
+            get "/bootstrap.json", headers: { Cookie: "locale=zh-CN" }
+            expect(response.status).to eq(200)
+            expect(response.parsed_body['bootstrap']['locale_script']).to end_with("zh_CN.js")
+          end
+        end
+      end
+
+      context 'when locale cookie is not set' do
+        it 'uses the site default locale' do
+          SiteSetting.allow_user_locale = true
+          SiteSetting.default_locale = 'en'
+
+          get "/bootstrap.json", headers: { Cookie: "" }
+          expect(response.status).to eq(200)
+          expect(response.parsed_body['bootstrap']['locale_script']).to end_with("en.js")
+        end
+      end
+    end
   end
 
   describe 'vary header' do