A lot of people do know Japanese. So they do know what is being sung. Even people like me who only know very little can still know what is being song, it's called translating the lyrics.
but... I go for music for sooooooooo many different reasons. Maybe I am sad and want a song that is sad to match my mood, like rain of lamentation, or maybe I want a hyper jumpy cute song, like Candy Baby, to get me in a better mood. Or maybe I want a dance song. I don't think I like any American song that is in my wii ddr, so I never play it, but I love Golden Sky and Honey punch when doing DDR at the movie theater. I love dancing to Love&Joy and Honey. I love random crazy exercize dancing to feat songs and there are a lot of Vocaloid feat songs I really like. I do like english songs too. And musical songs. oh, I like Red Hot Chili Peppers and some pink floyd. But also like Nightwish and Poets of the Fall or Gorillaz and TLC and Gwen Stefani and Seether and Lisa Loeb and Bjork and Michael Jackson and Wonder Girls and Billie Piper and Cindy Daniel and Tatu and ... well. A huge variety.
Listening to:
Idina Menzel Sings Defying Gravity