I just figured out how to do it, even though it's quite tedious.
When I want to restore a backup, I launch it, change the language, and click Back. This restores the backup and changes the language to French, so I can continue, but I think we need to find a way to lock the language chosen by the player so that it remains fixed until they change it.
Anyway, I'm going to continue playing this game, which I think is excellent, and I wish you all the best.