concern instead of rack::locale + fix user change with toasts

Gemfile

Gemfile.lock

app/controllers/application_controller.rb

app/controllers/concerns/with_locale.rb

app/controllers/users/confirmations_controller.rb

app/controllers/users/passwords_controller.rb

app/controllers/users/registrations_controller.rb

app/controllers/users/sessions_controller.rb

app/controllers/users/unlocks_controller.rb

config/application.rb

config/locales/en.yml

config/locales/fr.yml