That is most likely a bug/side-effect - although the compiler accepts them, it is not mentioned in the Release Notes, IDE doesn’t know about this, and non-Latin characters cause compilation errors on YYC on ~half of the platforms.
If it does become an officially supported feature, I can add support for it to GMEdit - will mostly need to figure out what is a valid letter now and what isn’t (e.g. µ counts as a valid variable name but ¶ doesn’t).