I don't know, but easy way to find out is to make the test in your sandbox env
Create an admin in command line (default language is english there)
bin/magento admin:user:create --admin-user='userTest' --admin-password='test123' --admin-email='test@test.fr' --admin-firstname='user' --admin-lastname='test'
With your current admin, do your language modification
Then connect to the newt created admin userTest and see if the language applies.
Though, you have to be aware that you will need to deploy static for the backend language too.
From my experience when salers have a one language store in front side, they tend to only deploy their website in that language and use the same language for the backend. But if you provide a different language for backend (english for example) then you will have to deploy en_US too.