update dutch l10n

A few changes.. not happy with all changes.. context and usage information could maybe help... 

Is there a possibility of a, fully functional, non-published test/playground environment?
To properly test the l10n I currently have to log in as a one of our clients... even then the string may not be used; depending on the client's account/subscription. Also I do not want to login as the client (asking for passwords is crap and embarrassing) ... ;-)