A few weeks ago Gmail started to auto-correct the text I type into its Chat window. This is a major problem for me, because I use Gmail in English but type in Hungarian as well, which then gets auto-corrected to similar English words. For example, if I type "gondoltam", it gets auto-corrected to "gondola" (which is an unrelated word).
The first time I noticed this, I opened Gmail's Settings and found a section for Autocorrect, which I subsequently set to "Autocorrect off". However, the text I type in Chat still gets auto-corrected. I also considered that it may be Firefox that does this, but I found no such feature or setting in Firefox. It also only happens in Gmail and not on other sites.
How can I disable this annoying behavior?
Not a duplicate
This is not a duplicate of How to disable permanently Gmail spell checker. That question is about spell checker settings for emails and this one is about autocorrect in Chat.