I don't see how people can learn a language by tests, which are only telling you if you did it right or wrong. I can see how this is used to verify the existing knowledge, but I don't see any usage in learning.
You learn a language by being exposed to it countless times, but most of us doesn't have the opportunity to be immersed 100% into a foreign language. Simple rules let us try out new sentences and do some self-checks to cull out the definitely wrong ones.
This makes your "training set" significantly larger without having to "collect that data". Of course it doesn't replace anything, but it is a useful part of the language learning journey, especially the early part. Later on, nothing can replace simple exposure.
This is more of a "quiz" format, not learning. There is a difference.
Right now it's hidden in a corner (iirc), so that i can barely see it. By showing the task and the answer next to each other when doing it wrong, the players might learn something of it.
What i typically recommend my students is to try to transform a learning task in a way that you need to apply a skill, without needing to do the skill itself.
For example playing english text adventure games is a very fun way to learn english. Players need to figure out what to enter using the keyboard and they use classical methods of figuring out the correct content (dictionary, translation) and they still have fun doing so. Even if it's hard work (not so much anymore with deepl etc, but back in the day it was). This can be applied to tons of tasks. - make sure you are not cheated when trading in a game. - keep up your reaction time by playing race games (a very good thing for elderly who want to keep theyr driving skills) - train your dictionary skills in scrabble. - ...