Allright, I've finished the MediaWiki core. That also includes MediaWiki (most used), MediaWiki 1.15 and MediaWiki 1.16 right?
If so, my work here is done :). Though every once in a while I'll pop by and do some more informal translations for MediaWiki extensions. There's no need for me to do nl-informal on Wikia extensions as these are already available at Wikia.
IMO your work isn't done. You've added the nl-informal messages to messaging.wikia.com in the 'nl' namespace, overruling the formal 'nl' messages from the extension files. Those should be removed, and nl-informal for the Wikia extensions should be made here.