I wonder why people are calling it Anime Music when they're actually just Japanese Music used as Anime Openings/Endings. Aside from the Soundtracks (aka BGM), they're pretty much sung by Japanese singers/bands.
Anyway, to answer that question... I have to admit, looking at my music collection, it's 90% Japanese Music (I also go for bands that haven't made a song for an anime as well if you need to know), so that's pretty much it. I do listen to English songs, but I'm too lazy to keep them in my folders and just go to the radio to listen to them, unlike Japanese songs that will never get played in the radio (aside from anime radio stations, but that doesn't exist here).