I thought it was strictly one character per 32-bit code.
Anyway, whatever it is called it is what wchar_t should be.
I do have some ideas for a better encoding (like, I assume, anyone competent with sufficient free time and interest in text encoding), but there's a lot of reluctance to put effort into something that's already completely eclipsed by a technically inferior but not completely unusable alternative, so I've had it mostly shelved.