Interesting phenomenon in this thread. On the one hand, many are decrying singers trying to adopt an accent that they don't come by naturally (e.g., a Yank trying to use an Irish accent when singing a song from Ireland).   On the other, many are saying it's "the worst" when someone from an Asian country tries to sing a song in English and can't pronounce the "r's" or "l's" properly.
So is the consensus that you should never sing a song in another language unless & until you can sound like a native speaker? Should middle-class professionals not try to sing blues -- or maybe sing blues with all the final "g's" clearly articulated (and maybe singing "I haven't got anybody" instead of "I ain' got nobody?")

Personally, I enjoy hearing singers sing songs in various languages and dialects other than their own, if the accent fits the song. Some songs really wouldn't sound right to me without being sung in a particular dialect. (Many English Music Hall songs come to mind.) Yet I would not want to discourage all but the "natives" to perform them.

I do agree, though, that some fake accents are strange concoctions of the imagination (e.g., the "Foghorn Leghorn" US "southern" accent) rather than honest attempts to mimic or echo an authentic accent one has heard.