Extract frontend_translations helper to support module (#34400)

spec/support/system_helpers.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 module SystemHelpers
+  FRONTEND_TRANSLATIONS = JSON.parse Rails.root.join('app', 'javascript', 'mastodon', 'locales', 'en.json').read
+
   def submit_button
     I18n.t('generic.save_changes')
   end
@@ -16,4 +18,8 @@ module SystemHelpers
   def css_id(record)
     "##{dom_id(record)}"
   end
+
+  def frontend_translations(key)
+    FRONTEND_TRANSLATIONS[key]
+  end
 end