It looks like you’ve made a good start. I tried it now with Japanese, and it worked pretty well. I wish you the best of success.
A few comments:
For Japanese, you might want to offer a choice for the amount of kanji to use in the written transcriptions that appear on the screen. Your current transcripts use the standard orthography, including kanji; some learners might like that, while others, especially beginners, will prefer that everything is in kana or romaji.
Other languages have similar aspects that should be customizable for learners: levels of politeness and formality, dialects and accents, grammatical gender, etc. It will be hard to do that with the current LLMs, but as better models become available it should become possible.
Multimodal LLMs that were trained on audio will be necessary for the tutors to respond to users’ pronunciation and intonation, produce natural backchanneling (an important part of conversation in Japanese and some other languages), etc. Perhaps such models will be available later this year.
Regarding gamification, how about offering choices to your users? Some learners will like gamification and benefit from it, while others don’t need it and will find it annoying.
It’s not clear from the free demo whether the characters one converses with are persistent or not. Especially for intermediate and advanced learners, it will be very valuable if your customers can chat with the same character repeatedly and that the character remembers the content of previous conversations and adapts accordingly. LLM context windows are getting longer, so that should be feasible. (Conversely, you will lose customers if they find that they are having the same conversations again and again or being encouraged to talk about things they aren't interested in.)
Also, you might consider setting up three-way conversations: two bots and the learner. One-on-one conversation practice can be tiring to the learner, and the learner doesn’t get a chance to observe how fluent speakers talk to each other. If the bots sometimes interacted with each other, the learner would both get a break and have a chance to learn by listening to the bots converse.
I have worked in language education for many years, and it seems that I was the first person to post a video to YouTube about using ChatGPT for language learning, on December 5, 2022 [1]. If you might find it useful to discuss ideas with me, feel free to get in touch. The URL of my website is in my profile.
[1] https://youtu.be/NVPHY3fYfmc