Language and pronounciation. You can really pronounce it however you want. It varies with the pronouncer's accent, etc.
The way Lavigne pronounces it is obviously anglicized. I have a friend called
Nadim whose name is pronounced [by everyone and now himself] NAY-deem not NAH-deem.
I adopted a cute lil' baby jesus fetus
from Fetusmart! Hooray fetus!