Ensure a valid locale is persisted during login

This action has to be performed here and not in I18nHelper, as spree_current_user is not initialized yet during the other checks / setting the selected locale value in the app

app/controllers/spree/user_sessions_controller.rb

@@ -6,11 +6,13 @@ module Spree
     include Spree::Core::ControllerHelpers::Common
     include Spree::Core::ControllerHelpers::Order
     include Spree::Core::ControllerHelpers::SSL
+    include I18nHelper
 
     ssl_required :new, :create, :destroy, :update
     ssl_allowed :login_bar
 
     before_action :set_checkout_redirect, only: :create
+    after_action :ensure_valid_locale, only: :create
 
     def create
       authenticate_spree_user!
@@ -48,5 +50,11 @@ module Spree
       redirect_to(session["spree_user_return_to"] || default)
       session["spree_user_return_to"] = nil
     end
+
+    def ensure_valid_locale
+      return unless spree_current_user && !available_locale?(spree_current_user.locale)
+
+      spree_current_user.update!(locale: I18n.default_locale)
+    end
   end
 end

spec/features/consumer/authentication_spec.rb

@@ -161,7 +161,7 @@ feature "Authentication", js: true do
           user.update!(locale: "xx")
         end
 
-        xit "logs in successfully and resets the user's locale to the default" do
+        it "logs in successfully and resets the user's locale to the default" do
           fill_in_and_submit_login_form(user)
           expect_logged_in