[ImpactBreaker]

Covering a song is no proof you speak perfect english. Artists like shiina ringo can cover english songs perfectly fine but have a problem when singing their own orginal english songs. When you hear a known song several times it's easy to pick the pronunciation and imitate it. Not saying that Jolin can't speak english though, as I never listened to her songs, she probably might be good at it, but I just want to point out that covers are not the best material to judge whether an artist is or isn't fluent in english. Of course you can actually tell those who clearly aren't good at english when they actually cover it with a terrible pronunciation, but the opposite is not a reliable parameter to judge in my opinion.