There's a set of rules used on domain names to stop homoglyph abuse there.[1][2] Applying those rules to language identifiers would prevent this problem. It's also useful to apply those rules to login names for forum/social systems. The rules prevent mixed language identifiers, mixed left to right and right to left text, and similar annoyances.

[1] https://tools.ietf.org/html/rfc5893 [2] http://unicode.org/reports/tr46/