I have noticed this when I was recording a WP demo for #1383:

And the first thing I thought was "Huh, ...scheduling theme changes! ...that's why WP is kicking our butts"
...but then I though "Wait a minute ...we have CMI in core ...we could schedule EVERYTHING!!!"

GitHub Issue #:
3185
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)