As someone also building a language-learning app for myself, it's not too hard to create an excellent app right now, but the "readily available" part of your requirements is now 10x harder than a few years ago. Users are getting bombarded by new apps, so marketing an app, which was already hard before AI, is now much, much harder.

I could try to market this app, but I tried that 2 years ago, and it was already essentially a failure. So I'm probably going to keep it for myself or just try to find a few users who like it and will use it for free.