slintpad.com uses the wasm port to run on a browser and is not the same as when using Slint to build a "native" app, especially on mobile.
Slint does support decent text input and IME. Including text selection with the native handle. As a demo for android you can try the demo from https://material.slint.dev/ ("Download APK")
https://docs.slint.dev/latest/docs/slint/guide/backends-and-...
But, I have only used it with Romanian and English.
Try here: https://slintpad.com/. (just replace the Text with TextInput) and see if it works.