FIX: adopt a simplified with_resolved_locale to ensure user's locale is always loaded

app/controllers/custom_wizard/wizard.rb

@@ -12,6 +12,7 @@ class CustomWizard::WizardController < ::ActionController::Base
   before_action :preload_wizard_json
   before_action :ensure_plugin_enabled
   before_action :ensure_logged_in, only: [:skip]
+  around_action :with_resolved_locale
 
   helper_method :wizard_page_title
   helper_method :wizard_theme_id
@@ -115,6 +116,13 @@ class CustomWizard::WizardController < ::ActionController::Base
     @preloaded[key] = json.gsub("</", "<\\/")
   end
 
+  ## Simplified version of with_resolved_locale in ApplicationController
+  def with_resolved_locale
+    locale = current_user ? current_user.effective_locale : SiteSetting.default_locale
+    I18n.ensure_all_loaded!
+    I18n.with_locale(locale) { yield }
+  end
+
   private
 
   def ensure_plugin_enabled