We should add the ability to specify an administrative language that gets used for all administrators. Essentially https://www.drupal.org/project/admin_language module.
Original issue from drupal.org: https://www.drupal.org/node/322995
My site's default language is Finnish but I need to use English for admin pages. There should be next to Default language option the second one where user could choose the admin language. I tried also to change language from my user account but it didn't make any change (bug?).
This patch is actually quite trivial and being from 2012 is almost directly applicable to Backdrop.