Context: I speak Chinese, I'm a high school student from the Philippines. We're a Chinese-Filipino international school. Our school treats the HSK test as a benchmark every year. For a batch of students to graduate, they'd have to pass a specific HSK level (e.g. I'm Batch 2019, I have to pass HSK 3 to graduate).

1. I see this as an app our Chinese teachers would recommend, seems a design they'd go for. However, for us students, I'd use it but the orange color seems to drained? Perhaps making it a bit brighter, I think even a white background with a few elements around would / could suffice?

2. A bit too text-based? Maybe you're going for simplicity? But if I were to use a language learning app, I'd want one that I'd be hooked into. Perhaps having a point / incentives system?

3. I think the interface should be modified to look more like an iOS app. Perhaps with tabs or something, because based on the screenshots, it looks like an app like that would be better of on the web.

4. The panda is a bit cute. Contrary to other comments, I think some students would like it, but better make it dynamic to be more attractive.

That's all for now, I'll take a deeper look soon and come back with more. Good luck in building and shipping your product!

Portability? I guess it depends on who you are targeting and what you want your customers to do with your app. If it's a phone app, most likely it can work offline and on mobile. In addition, if you have a phone app, word can be easily spread about it. Personally, I would tell my friends about this cool app I got on my phone, but not about a website I just visited.

Avenir Next - has many styles and potentially useful in a lot of different use cases.