However, soon I found that pasting CJK brings question marks. A tip suggests setting
__CF_USER_TEXT_ENCODING, which doesn't work for me. I ended up changing the content of
0x8000100:0x8000100. After reboot, copying and pasting CJK just works (TM).
But something strange hits me. Quite a few shortcuts involving Command doesn't work in Firefox and KeePassXC. With some trial and error, it turns out modified
~/.CFUserTextEncoding broke things. I have no choice but changing it back.
KeePassXC uses QShortcut and Firefox appears to use Cocoa directly. What stops them from working? Dunno.
0x8000100 is exactly UTF-8. So, another amazing story of macOS: using UTF-8 as the default encoding can break things!