Thanks. Didn't think of that. Do you have a suggestion of what character I could use for Cyrillic keyboard layout or others?

Ideally, you shouldn't rely on characters for this, you should instead use the key code (which is 90 for z/я), which identifies the physical key on the keyboard as opposed to its corresponding character in the current layout.

Here's a useful tool for finding out key codes: https://www.toptal.com/developers/keycode