Currently, when a Chinese input method is activated (e.g. Microsoft Pinyin), typing by the VirtualKeyboard can only type in English characters, which looks like the key-press message just bypasses the IME and reach the textbox directly. Both first-party IMEs provided by Microsoft and third-party IMEs were tested.
I guess Japanese and Korean IMEs are affected as well, as they all need an IME program to convert codes to characters. Supporting the East Asian IMEs may help greatly for touch-screen apps running in these cultures. Otherwise, the users can type in English only.
How to add a Chinese IME:
1. Add Chinese (China) language in Settings -> Time and Language -> Language.
2. In the Options of the Chinese language in the language list, click Add Keyboard and select Microsoft Pinyin.