i18n sign in

app/controllers/application_controller.rb

@@ -52,7 +52,8 @@ class ApplicationController < ActionController::Base
   private
 
   def with_browser_locale(&)
-    locale = request.env['HTTP_ACCEPT_LANGUAGE'].to_s[BROWSER_LOCALE_REGEXP].to_s
+    locale   = params[:lang].presence
+    locale ||= request.env['HTTP_ACCEPT_LANGUAGE'].to_s[BROWSER_LOCALE_REGEXP].to_s
 
     locale =
       if locale.starts_with?('en-') && locale != 'en-US'

app/controllers/sessions_controller.rb

@@ -3,6 +3,8 @@
 class SessionsController < Devise::SessionsController
   before_action :configure_permitted_parameters
 
+  around_action :with_browser_locale
+
   def create
     email = sign_in_params[:email].to_s.downcase