As someone who's bilingual (English, Chinese) and have taught both languages before, my suggestion is: You are focusing on the easier part of learning a langua

As someone who's bilingual (English, Chinese) and have taught both languages before, my suggestion is: You are focusing on the easier part of learning a language - listening and reading. All of my past students struggled far more with pronouncing and writing. Of course recording the users' pronunciations and handwritings, and then verifying them is a lot more technically challenging, but still doable. It will surely impress a lot of people. (Maybe that's in your long term plan?) Not saying what you made is not useful, it certainly is. But it's not where the pain is in learning a language. Depending on the curriculum, it may not make that much of a difference on each student's language ability. But then again, our current education system is not making that much of a difference either.