User's can now have an administration specific language preference

In Drupal 7, people could install the Administration language module (http://drupal.org/project/admin_language) to set their administration pages to a specific language. In Drupal 8, we went a bit ahead and made this a language negotiation provider with per-user settings, so different accounts can view administration pages in different preferred languages, each as suitable for site administration based on their language knowledge.

A new Account administration pages negotiation setting was added on the language detection and selection page:

A setting was added to user accounts to specify their preferred language for site administration: