>has no idea if what they're writing makes sense or if there's any subtle mistakes

These days AI can tell you if it makes sense and the subtle mistakes you are making. I think this view point is outdated now that everyone has a personal language tutor in their pocket.

I've used several LLMs to do translations and they're very hit/miss, specially in very high context languages like japanese. I'm not sure recommending their usage for a beginner is good advice, it's better than nothing for sure, but still not a replacement for a human coach.