I use multilingual keyboard layouts, so I know that at least on Windows the selected layout is specific to each window. If I chat with someone in one language, then switch to my IDE, it will not keep the layout I used in the chat window.
But I also have accidently hit the combination to change layouts while doing something, so it can happen. I’m just surprised that Cyrillic с is on the same key as C, instead of S.
I’ll never understand consuming this type of information in video format.