This is basically to consider improving the option select elements that we've added in Backdrop core v1.12.0 (see #1005) to include the functionality of https://www.drupal.org/project/select_option_sort, which allows sorting the options in the select element by key (if the "Custom keys" checkbox is ticked) or value, and also ascending/descending.
Before:

After (suggested mockup):

GitHub Issue #:
5823
Recent comments
There is a Drupal 7 contrib module that "lets the administrator see all administration pages in her preferred language" and which could be ported to Backdrop: https://www.drupal.org/project/...
Allow admin to select admin language seperate from front end language (multilingual)
@stpaultim – You're right: my approach affects also the main menu. I guess, because menus are also considered as user interface (not as content). @findlabnet – If I didn't miss anything,...
Allow admin to select admin language seperate from front end language (multilingual)
Go to the account edit of the desired user. On the horizontal tab below "Region and Language," select "English" or another language. WFM.
Allow admin to select admin language seperate from front end language (multilingual)