I started listening to japanese music in order to improve my language skill. Even though I'm currently studying Japanese at university, I still find difficult to translate song lyrics, but at the same time I feel guilty for listening to certain songs without having a clue about the meaning. I feel like I can fully appreciate artists' effort. Regarding screamers, in my experience at a certain point you can understand what they are saying - at least, some lines - but, yeah, maybe you are right saying that in this genre you are more focus on other things that on the song content. As far as I'm concerned, I must admit that, while I'm listening to Japanese music, I'm usually more focused on the sound and the visual than on the meaning.