Linux has a checkpatch.pl. If it doesn't already test for Unicode identifiers, it would be trivial to add that. This is a non-issue. You don't ban a new version of a language just because it allows some undesirable things; it's trivial to ban those things specifically, either with scripting or specific compiler option overrides.

Heck, Linux already uses GCC plug-ins to implement some fancier security stuff; it is silly to think they can't handle forbidding Unicode identifiers.