Rails | Devise | Internationalization I18n

If you are upgrading your app from uni-lingual to bilingual, you might want to have separate pages for Devise related pages as well. Its simple for simpler implementation of devise like no ‘omniauth’. But if you are including ‘omniauth’ then normal recommended approach will not work.

# Before
devise_for :users, path: '',
  path_names: { sign_up: :signup, sign_in: :login, sign_out: :logout },
  controllers: {
    registrations:      'devise_override/registrations',
    confirmations:      'devise_override/confirmations',
    sessions:           'devise_override/sessions',
    omniauth_callbacks: 'vehicle_owners/omniauth_callbacks'
  }

# After
devise_for :users, only: :omniauth_callbacks, controllers: {omniauth_callbacks: 'vehicle_owners/omniauth_callbacks'}
scope "(:locale)", locale: /en|fi/ do
  devise_for :users, path: '',
             path_names:   { sign_up: :signup, sign_in: :login, sign_out: :logout },
             controllers:  {
                 registrations:      'devise_override/registrations',
                 confirmations:      'devise_override/confirmations',
                 sessions:           'devise_override/sessions'
             }, skip: :omniauth_callbacks

So, it turns out that you cannot scope the Omniauth related URLs, as it makes no sense. You might also see warnings like

Devise does not support scoping OmniAuth callbacks under a dynamic segment
and you have set "/(:locale)/". You can work around by passing
`skip: :omniauth_callbacks` to the `devise_for` call and extract omniauth
options to another `devise_for` call outside the scope. Here is an example:

 devise_for :users, only: :omniauth_callbacks, controllers: {omniauth_callbacks: 'users/omniauth_callbacks'}

 scope '/(:locale)', locale: /ru|en/ do
   devise_for :users, skip: :omniauth_callbacks
 end

Note: Do not forget to restart the application after any major changes.