hey Andrew,
I am really sorry that delay of this reply,
I already tested 3~4 times in your site, this is what I tested just now :
Case 1 :
Make sure group creator/admin set language use `default` or `dutch` from their user profile (screenshot :
http://screencast.com/t/tkAUnACFu2 ).
So when the group creator already submit a new group, the system will check which is current site language he logged in to.
If that is Dutch site language, system will send out Dutch language email content.
If admin logged in backend (Dutch language) and click on approve button from group moderation page, the system will send out Dutch language email content. (you can check first and second screenshot below)
Case 2 :
If admin logged in backend (English language) and click on approve button from group moderation page, the system will send out English language email content. (you can check the third and fourth screenshot below)
Can you give it a try again and see is it correct this behaviour?