Errors in commands containing UTF8 characters are printed with UTF8 byte expansion

[Yuri]

When I accidentally type some nonexistent command containing UTF8 
characters, an error has UTF8 characters expanded:
$ ЫZZZ
bash: $'\320\253ZZZ': command not found

I think bash shouldn't discriminate against UTF8 characters in error 
messages, and shouldn't expand them. If some international users wish to 
have UTF8 in their commands, bash should preserve them in all messages.

My LANG is en_US.UTF-8, and changing it to ru_RU.UTF-8 doesn't seem to 
make a difference. Same with LC_ALL.

bash-4.2.45_1

Yuri