#428

backend/app/controllers/application_controller.rb

@@ -10,6 +10,7 @@ class ApplicationController < ActionController::API
   before_action :reject_banned_ip_address!
   before_action :authenticate_user
   before_action :reject_banned_user!
+  before_action :validate_explicit_locale!
 
   def current_user = @current_user
 
@@ -99,6 +100,8 @@ class ApplicationController < ActionController::API
   end
 
   def resolve_locale!
+    return @resolved_locale if defined?(@resolved_locale)
+
     code = params.fetch(:locale, 'ja')
     unless code.is_a?(String) && Locale.codes.value?(code)
       raise UnsupportedLocale
@@ -107,6 +110,10 @@ class ApplicationController < ActionController::API
     locale = Locale.find_by(code:)
     raise UnsupportedLocale unless locale && locale.deprecated_at.nil?
 
-    locale
+    @resolved_locale = locale
+  end
+
+  def validate_explicit_locale!
+    resolve_locale! if params.key?(:locale)
   end
 end