since 20w17a, Minecraft supports non-BMP characters (like emojis and some CJK characters) but most of them are still tofus in the game.

How to reproduce:

1. Open the chat
2. Copy this character "𡂿" (it's a CJK-B character)
3. See a tofu but excepted a proper Chinese character.

Also, until now, all the CJK characters use the glyphs from Simplified Chinese Standard, which is not suitable for other languages (e.g. Japanese). Maybe it's the time to fix it as well (like the game will use the Japanese variant when choosing Japanese, CNS11643 for Traditional Chinese, GB18030 (the current standard that Minecraft is using) for Simplified Chinese, Korean standard for Korean, etc.).

The spreadsheet is from here.