The app is optimized on the whole population, not on individual level. They even publish papers on global optimization.

These kinds of learning apps are destined to become mediocre over time.

The learning metric is so easy to capture, the learning content so easy to produce, yet no one has an individualized loop to make learning work well.

For example, I'd press "Training" on Duolingo, and would get nowhere. Same lessons all of the time. Bread and water.

Duolingo is laughably inefficient. I have an app I've made for myself to learn french, and it's amazing how little effort is required to make something 10x better. (I completed the french Duolingo tree and learned essentially nothing so I feel justified in saying that.) If you're learning french, let me know and I'll add you to the app.

The real question: the 10x, can you mainstream it ? Or is it only 10x better per your preference ?

Btw: if the app is available, I would love to take a look!

Yes, we've spent a lot of time getting the STT and TTS to work seamlessly in multilingual, it works pretty well!

I said I would use it and report back. Unfortunately, the experience was not great for me. I told it multiple times I'm a beginner and not speak in full, long sentences in my target language, and it would remember that for one response maybe, then switch right back to full sentences. I had to keep telling it I couldn't understand it and that I'm a beginner. After the 4th or 5th time I gave up.

Babbel is better than Duolingo!

Unfortunately, Babbel doesn't have a Hindi course. I wish it did.