FIX: Use correct locale for error messages (#10776)

Error messages for exceeded rate limits and invalid parameters always used the English locale instead of the default locale or the current user's locale.

app/controllers/application_controller.rb

@@ -152,14 +152,16 @@ class ApplicationController < ActionController::Base
   rescue_from RateLimiter::LimitExceeded do |e|
     retry_time_in_seconds = e&.available_in
 
+    with_resolved_locale do
       render_json_error(
         e.description,
         type: :rate_limit,
         status: 429,
         extras: { wait_seconds: retry_time_in_seconds },
-      headers: { 'Retry-After': retry_time_in_seconds },
+        headers: { 'Retry-After': retry_time_in_seconds }
       )
     end
+  end
 
   rescue_from Discourse::NotLoggedIn do |e|
     if (request.format && request.format.json?) || request.xhr? || !request.get?
@@ -170,11 +172,15 @@ class ApplicationController < ActionController::Base
   end
 
   rescue_from Discourse::InvalidParameters do |e|
-    message = I18n.t('invalid_params', message: e.message)
+    opts = {
+      custom_message: 'invalid_params',
+      custom_message_params: { message: e.message }
+    }
+
     if (request.format && request.format.json?) || request.xhr? || !request.get?
-      rescue_discourse_actions(:invalid_parameters, 400, include_ember: true, custom_message_translated: message)
+      rescue_discourse_actions(:invalid_parameters, 400, opts.merge(include_ember: true))
     else
-      rescue_discourse_actions(:not_found, 400, custom_message_translated: message)
+      rescue_discourse_actions(:not_found, 400, opts)
     end
   end
 
@@ -238,10 +244,8 @@ class ApplicationController < ActionController::Base
 
     message = title = nil
     with_resolved_locale(check_current_user: false) do
-      if opts[:custom_message_translated]
-        title = message = opts[:custom_message_translated]
-      elsif opts[:custom_message]
-        title = message = I18n.t(opts[:custom_message])
+      if opts[:custom_message]
+        title = message = I18n.t(opts[:custom_message], opts[:custom_message_params] || {})
       else
         message = I18n.t(type)
         if status_code == 403
@@ -329,8 +333,8 @@ class ApplicationController < ActionController::Base
   end
 
   def with_resolved_locale(check_current_user: true)
-    if check_current_user && current_user
-      locale = current_user.effective_locale
+    if check_current_user && (user = current_user rescue nil)
+      locale = user.effective_locale
     else
       if SiteSetting.set_locale_from_accept_language_header
         locale = locale_from_header

spec/requests/application_controller_spec.rb

@@ -647,6 +647,58 @@ RSpec.describe ApplicationController do
     expect(response.body).to have_tag("link", with: { rel: "canonical", href: "http://test.localhost/t/#{topic.slug}/#{topic.id}" })
   end
 
+  context "default locale" do
+    before do
+      SiteSetting.default_locale = :fr
+      sign_in(Fabricate(:user))
+    end
+
+    after do
+      I18n.reload!
+    end
+
+    context "with rate limits" do
+      before { RateLimiter.enable }
+      after { RateLimiter.disable }
+
+      it "serves a LimitExceeded error in the preferred locale" do
+        SiteSetting.max_likes_per_day = 1
+        post1 = Fabricate(:post)
+        post2 = Fabricate(:post)
+        override = TranslationOverride.create(
+          locale: "fr",
+          translation_key: "rate_limiter.by_type.create_like",
+          value: "French LimitExceeded error message"
+        )
+        I18n.reload!
+
+        post "/post_actions.json", params: {
+          id: post1.id, post_action_type_id: PostActionType.types[:like]
+        }
+        expect(response.status).to eq(200)
+
+        post "/post_actions.json", params: {
+          id: post2.id, post_action_type_id: PostActionType.types[:like]
+        }
+        expect(response.status).to eq(429)
+        expect(response.parsed_body["errors"].first).to eq(override.value)
+      end
+    end
+
+    it "serves an InvalidParameters error with the default locale" do
+      override = TranslationOverride.create(
+        locale: "fr",
+        translation_key: "invalid_params",
+        value: "French InvalidParameters error message"
+      )
+      I18n.reload!
+
+      get "/search.json", params: { q: "hello\0hello" }
+      expect(response.status).to eq(400)
+      expect(response.parsed_body["errors"].first).to eq(override.value)
+    end
+  end
+
   describe "set_locale" do
     # Using /bootstrap.json because it returns a locale-dependent value
     def headers(locale)