Use case: wipe data from test installation in order to start over quickly...
1. drop/empty the db
2. delete ./files and its contents
3. delete settings.php
4. visit site to re-start the installation process
As it is now, the installer complains about a missing settings.php:

So I had to extract a fresh copy of the file in order to carry on. Can we ship a default-settings.php file and have the installer create a copy of it instead of complaining in this case?
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)