I know people may want to use it to express their identity, but I think as far as possible we should be in the business of dealing with communication and intelligibility.

There are cases that may be more relevant to distinguish - so languages that can be written in various character sets (Azerbaijani in Latin characters vs Azerbaijani in Cyrillic characters vs Azerbaijani in Arabic characters) it may be well worth searching separately. But this might be something we need to find out by trial-and-error.

I agree, basically, with your analogy to mood-icons - let people display it however they like, but have metadata that's in a reasonably restricted format for ease of searching.