Terry J. Reedy, Japaneese has no cyrillic characters, it's alphabet consists of hieroglyphs and it has nothing to do with Ukrainian even if it looks the same for you.
"about Windows' built-in Cyrillic IMEs and control key combinations?"
In depth - no. I'm just using them and I know that Python is the only program I've ever met that doesn't exept same combinations with Ukrainian or Russian language on.
If you want to test what I'm talking about - just temporary add to your languages on your PC Ukrainian language, open Python IDLE and try any shortcuts while input language is Ukrainian.
Cyrillic characters can have sometimes problems with encoding, because they are not included to default ASCII table, only to extended versionis. Could that be a reason?
Or I just don't understand something? If not, please explain or give me a link or tip where can I find out what's goind on and who can fix it. Thanks.