I am typing into my terminal and the stdin is changing and adding characters on its own

Solution 1:

I don't have any problem with trying to paste that line into zsh running in Terminal.app. Some testing...

zsh: processed normally
dash: processed normally
oksh: processed normally
pdksh: processed normally
tcsh: processed normally
bash: processed normally
fish: processed normally
ksh: takes the Chinese as editor commands and weirds out

I'll report that as a ksh bug, I suppose.

But your problem would seem to be OhMyZsh, not Terminal.app. I can replicate the ksh behavior in iTerm as well.

Edit: ksh has a bug with multibyte characters and the KEYBD trap. See https://github.com/ksh93/ksh/issues/307 and https://github.com/att/ast/issues/197