Store locale in a user's field and switch locale on mailers

app/mailers/devise_mailer.rb

@@ -0,0 +1,13 @@
+class DeviseMailer < Devise::Mailer
+  helper :application
+  include Devise::Controllers::UrlHelpers
+  default template_path: 'devise/mailer'
+
+  protected
+
+  def devise_mail(record, action, opts={})
+    I18n.with_locale record.locale do
+      super(record, action, opts)
+    end
+  end
+end