An undocumented Gmail search operator,
language: (or simply
lang:), finds messages by the language they're written in. Give it a try in your inbox:
lang:Arabic both turn up several messages in the Lifehacker tips box. Sadly
-lang:English doesn't seem to work, which would be perfect to create a filter for all messages not in English; but you can create filters to snag messages in particular languages you don't speak, for instance.