edit activation mail

Hi Team,

We installed a WP MU with Buddypress. It works fine.
But I like to edit the activation mail:
"Thanks for registering! To complete the activation of your account and blog, please click the following link:
http://activate?hjgkhf

After you activate, you can visit your blog here:
http://stijntemplate1.tnxt.nl/ "

I've been searching for hours now, but I still can't find it.
I already changed the buddypress language. That works fine for the pages, but nog for the activation mail.

Do you have a solution?

Thank you so much!

Cheers, Stijn