I alternate between sticking the original name right after the English or Romanized name, or using the subtitle field for it. I might just start using something like an ORIGINALTITLE, ORIGINALARTIST, ORIGINALALBUM, etc., for untranslated names. (I think it'd be too much trouble to have regular tags being original, then translated names as EN_TITLE, RU_TITLE, etc., especially with mobile players, but maybe that's the better option.) And yes, it IS important for me to keep the original.
Album: The Tale of Princess Kaguya かぐや姫の物語
Artist: Joe Hisaishi 久石 譲
Track 1: Overture はじまり
Track 2: Light 光り
Opinions? Has anyone come up with good tags, or even bothered?