[suzakus]

Native as in Swift/Objective C (iOS) or Kotlin/Java (Android). Probably 99% of the UI (and lower layers, outside of specialty cases!) is based in that. C++ is used for typical high performance cases; e.g. Video rendering (though there's more than that).

There's a lot of internal tools. I don't know what they're written in. I would not be surprised if it's Lynx, but I'm a mobile developer on the TikTok app, and haven't ever looked into it.

I haven't come across any WASM in my time here, but I'm not in a position to declare that it doesn't exist.