<Cyrillic_schwa> is undefined

[Baurzhan Ismagulov]

Hello,

I can use emacs cvs with pt154 encoding on the Linux console. However,
when I type some Cyrillic characters under X, emacs says, e.g.,
"<Cyrillic_schwa> is undefined".

I see that this message comes from src/keyboard.c, however, I couldn't
figure out how the character is processed.

I want to add support for the missing characters, where should I look?

Thanks in advance,
Baurzhan.