Hello, I am looking for a Dutch translation for my forum. Can someone assist me with this?

There are only 3 Dutch translations in the Marketplace: https://invisioncommunity.com/files/category/161-translations/

 

2 of them are for 4.4, and the most recent one is updated for  4.7.3 (so it's 10 versions behind the current 4.7.13):

 

Maybe you can try contacting the author to see if he has any plans to update it further.