Changing language used in "Membership"

Hi
I am building a site ( http://www.fendano.nl) using Membership.

The site is in Dutch and the Membership plug in gives "subscription" and "payment" responses in English.

Sample: http://fendano.nl/index.php/register/
-> Please check the details of your subscription below and click on the relevant button to complete the subscription.

How/where can I translate/change the texts to "Dutch" so the customers get to see Dutch "system responses"...

Thanks.
Frank