Nice job. As someone who practices foreign languages daily and is also a huge fan of the New York Times daily crossword, I'll offer some feedback.

This is essentially more of a "projection" of the standard question/answer format and misses what makes crosswords engaging: the clues.

Since the clues are basically just straight definitions, they’re just never going to be very interesting. You could try using an LLM to dynamically generate more interesting clues that still lead you to the target word you’re studying, but then you have to factor in costs/etc.

> Works with any language (I think).

Well... no. It's obviously going to work with a logographic language like Chinese.