Delegate Account#user_locale method and allow nil (#2927)

app/lib/language_detector.rb

@@ -35,6 +35,6 @@ class LanguageDetector
   end
 
   def default_locale
-    account&.user&.locale || I18n.default_locale
+    account&.user_locale || I18n.default_locale
   end
 end

app/mailers/notification_mailer.rb

@@ -71,7 +71,7 @@ class NotificationMailer < ApplicationMailer
   private
 
   def locale_for_account(account)
-    I18n.with_locale(account.user.locale || I18n.default_locale) do
+    I18n.with_locale(account.user_locale || I18n.default_locale) do
       yield
     end
   end

app/models/account.rb

@@ -111,6 +111,7 @@ class Account < ApplicationRecord
            :current_sign_in_ip,
            :current_sign_in_at,
            :confirmed?,
+           :locale,
            to: :user,
            prefix: true,
            allow_nil: true