Is there any way I can copy Cyrylic letters from the OS to in-game chat and vice versa? If I copy it into the game, all I get is a bunch of question marks. The other direction causes problems too. No matter what's the problem with characters encoding, there's not much I can do.

I don't think so. The problem is that, when you copy the russian text into LFS, it has a different codepage than LFS. That's why you get gibberish text after pasting the russian text.

You can use LFSLazy for that :P

In LFSLazy window you can copy messages by pressing right click->Copy


And paste it anywhere


Other direction should be possible as well, by entering text to Chat Input below that list and it does work for most codepages, but for some reason it wasn't so succesful with Russian which I plan to look at soon.

There is a Windows setting something like "Code page for non-unicode programs".

If this is set to Cyrillic then you should be able to copy and paste Cyrillic text. Unfortunately it's a system wide setting and not per program.