I don't speak Russian, and probably many users don't. Should there be some way to send flagged messages in chat that need to be reviewed and aren't in English preferentially to users who are more likely than average to be able to read it? Perhaps based on membership in sites related to those languages?
I could have sworn its come up a few times - mostly with the $lang.so sites.
These are a pain, and at least as moderators go we often leave them until a 'native language' moderator (not necessarily for the site).
Language detection is hard. I often do a quick triage with google translate and it sometimes misdetects the language - and these are dedicated tools for the job. (Relatedly, someone suggested autotranslating flags - and many of the problems and solutions seem to fit here too).
And its hard to work out who can speak/read a language well enough to moderate. Many of these communities are smaller - if you prioritised 10k and mods for say, the russian SO site, they'd be folks already in the room, and seeing both the flags, and context and able to deal with it. Though, that makes me wonder if adding a "kick" style warning and BONG to the room for mods, 10kers and ROs when there's a flag would help. Ideally just for the room, though in theory you might do it for rooms associated with the relevant site.
As for languages with no sites associated, though. You're just going to have to remember who speaks what, and hope they're around. There's no flag on SE that indicates I can read tamil, both badly transliterated, and in the proper script.