What language is that? Given that there are glyphs for Ancient Egyptian in Unicode now, the claim that there's a language you can't write in Unicode needs some backing :)
I presume they mean Han unification[0], which to an uneducated outsider sure sounds like a fuckup. I wonder if it's possible to fix it inside Unicode without throwing the rest of it away. Reserve new blocks for all the needed graphemes and deprecate the unified ones?
Japanese. If you try to write it in Unicode you get (in the overwhelming majority of applications) Chinese and some vaporware excuses about font regions.