Very nice!
I think it's great to be able to talk about any topic, hopefully something interesting, while you also learn a language.
What I really want from this is more study tools available inline in the conversation. Getting a translation of the whole response is cool, but often I just want to know one word or a phrase. Or in turn I want to say something and I am missing one word of vocabulary to say it.
I got along using Siri, which worked a little but it's not great. I've used Google Translate in another tab in other similar experiments. I think it's actually good that there's some friction... learning should be a bit of a struggle, you should be pushing yourself. But not too much, and the right kind of struggle! Figuring that out is really where this product could shine.
For instance, when I type a response it might be nice to see a critique. It could be little things (lots of forgotten accents), or other comments. Using GPT you can probably get much more sophisticated feedback, like suggestions that a particular word might be a literal translation of the intended meaning, but isn't the right word to use in that context. Some of this help is just right, for other people it's not meeting them where they are, so I can imagine some might be indicators that feedback is available (without showing it), or... well, lots of ways to present things.
One way to create useful friction might also be to make the tools helpful but not automated. Want to look up a word? You can type it in English and it'll show you the translated word... but you have to type it in. Maybe even word lookup could work that way? The obvious lookup is to click or hover over a word, but maybe you should have to type the word you are looking up (or eventually say the word). But the translation should still take the context into account!