that is an interesting point - which is why I asked it since obviously there's not a single definitive answer of what makes a kpop idol a kpop idol
maybe one of the requirements is singing in korean or (at least partially in korean) but maybe there are others as well (or not...)
the way I put it is merely singing an original song in a particular language doesn't make you an idol of the language of that country - for example there are lots of kpop groups who sing a song or two in japanese even original songs - I would hardly consider them to be jpop no?
there are also idols that sing english songs but that doesn't make them US artists?
a few groups have even done songs in other languages I like Super Junior in spanish and SNSD in chinese but I wouldn't consider them latin artists or Cpop...
and the other thing I'll add is obviously not everyone who sings in korean in korea is an idol - there's lots of other genres of music for example trotists aren't idols per se therefore there is a different between an "idol" and people who are in groups or other soloists but not idols