This is the respective issue for the feature that went into D10.1.x core with https://git.drupalcode.org/project/drupal/-/commit/4dbf3f46c19766a38c3e4... (issue | change record).
Problem/Motivation
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Use case: As a site moderator, I'm able to use a View, located at /articles/moderate, with VBO to bulk approve/decline articles. I want to access this moderation tool using the admin theme in the same way I'm using the node edit page.
Proposed resolution
Add a new page setting "Use the administration theme" in the page display that allows site builders to make that page an admin one, similar to https://www.drupal.org/project/page_manager.
User interface changes
- View edit page: Page settings

- View edit page: Page settings (with an admin/* path)

- Modal 'Administration theme' form

- Modal 'Administration theme' form (with an admin/* path)

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)