I quickly tried it and looked at the code.
It filter the languages available for the user with the new field in the profile of the user.

So in the language switcher of Polylang in the WordPress Admin bar, the user only see the language which is available for him. , great !

But I can continue to choose “Show all languages” and the user is not filtered by the only language available. I succeeded to edit a post or page in another language than the restricted one.

This plugin is well coded but does not the jo for me. It misses some things to do it completely.