sizonov_stas That'd be awesome!
I think the discussion on github has taken a different turn with people suggesting that flarum should provide an option in the admin panel to have the url in the native language or with mapped letters!
From an SEO perspective I'm pretty sure (though not an expert) that mapping would do a better job.
Plus if you head out to do this right now it'll take more time to solve a simple problem, than it'd take to provide the mapping for now and later on an option to choose!
That's just my opinion though!