How can I translate string templates in Metatag module?
Basic internationalization support can be found in the i18n module:


  All default configurations may be translated using the
  Internationalization (i18n) module. The custom strings that are
  assigned to e.g. the "Global: Front page" configuration will show up
  in the Translate Interface admin page
  (admin/config/regional/translate/translate) and may be customized per
  language.


There exists at least 1 ongoing issue in Review still with Views, Panels and other 3rd party contrib modules and the metatags module.