I don't know what did I do but now when I want to write something in the chat it only appears korean or japanese letters (Ｉ　吃　); I don't know.

Does anybody know how can I change it?

Thank you

PS: I wrote this in Word and the I pasted it here.

It's possible that you have a hotkey that you pressed to change keyboard language.
You could check Control Panel / Regional and Language Options / Languages / Details / Key Settings for the hotkeys you have configured.

Or if you have a language bar up running, I think Alt-Left Shift changes languages, so you might have pressed something that locked your browser to use a specific language.

Thank you Boris, you solved it!

It was weird because I could write in Chrome but not in Mozilla, so I should have changed something in this browser, but I didn't know how to fix it.