Interesting, the thing is I have tried this. I can very easily do the same for a Japanese song but that's because I at least know the phonetics of the language. And from watching 100s of subtitled anime. I don't actually know what they are saying, but I can sing along. Same with Spanish since I learned that throughout grade school.
I struggle to do the same with Korean which is why I mentioned at least learning some basics, maybe I'm just not trying hard enough lol.
I have the same problem with Korean for some reason. There are a few songs that are easy for me to imitate, but often I'm lost. I guess maybe the pace is too fast then and I can't distinguish the words without knowing some phonetics.
I learned the alphabet some time ago and it helps identifying groups, song names and idol names.
I'd like to get more into it, because I do think it's a beautiful language.