I watched the demo video. Obviously you're going to need to write language lessons for the avatar to deliver. I'm not sure what your background is but do you know how you'll do that? Many apps hand that job over to AI and that might work fine for a beginner lesson 1 when you're just repeating some simple phrases but how would it manage with a properly structured lesson about the present perfect or subjunctive? I've seen AI give incorrect information about grammar and create quiz questions that are wrong or impossible to answer.

Also, language lessons don't just exist in isolation, a good language course ties each lesson together to reinforce what was previously learnt. You would have to think about all this.

Your other alternative is straight-forward conversation practice for higher levels, where you're not actually teaching the language, just providing conversation. But I think that very soon ChatGPT will have human-like avatars in their interface, so people will be able to use that for conversation practice.

You're probably aware, but other apps that are doing something similar are Praktika, Loora, Call Annie, Makes You Fluent.

If you want to do some more reading about the AI language learning industry you may find my Medium articles useful: https://medium.com/@oh-yeah-sarah