Allow setting of default language through config

Setting of locale in controller extracted to Localized concern,
the doorkeeper authorized applications controller moved under
custom namespace with inclusion of Localized, which resolves the
"it sometimes appears in a different random language" bug

config/routes.rb

@@ -11,7 +11,7 @@ Rails.application.routes.draw do
   end
 
   use_doorkeeper do
-    controllers authorizations: 'oauth/authorizations'
+    controllers authorizations: 'oauth/authorizations', authorized_applications: 'oauth/authorized_applications'
   end
 
   get '.well-known/host-meta', to: 'xrd#host_meta', as: :host_meta