From your account page, under the "Books to Mail" tab at the bottom there is a button to cancel the request if you haven't printed the wrapper. 

Why do you think the requester might not have not have known the books were in German?  Isn't that obvious from the title, description or ISBNs? 

Earlier this week I accepted a request, but then I noticed there was some slight water damage to the introductory pages of the book (just the review excerpts and author's acknowledgements -- the part of the book with the story is fine).  :-(  I PMed the requester and explained the situation, and offered to either cancel the request and pull the book from my bookshelf or send him/her another book of his/her choice from my bookshelf for free.  Based on similar situations I have read about here, I asked him/her to let me know within 48 hours since that was how long PBS said I had to mail the book.  (I forgot about the grace period, still, either way, I'd like to resolve this.)  I still haven't heard from the person, but once the 48 hours is up, if I still haven't heard from them, I'm canceling the request and offering the book as an unpostable with another order. 

Since you didn't give him a deadline, your situation is a little trickier, but if you haven't heard from him in 2 days, I would send the books.  He did request them, they meet PBS guidelines. 

Kirstin;  this is from The Help Center.  You CAN cancel before or after  you accept:

To cancel/decline a request:

• If you have not yet accepted the request:

• Log into PBS, go to My Account   and click on the request.

• If this is a Bulk (multiple-book) request, and you can send SOME books but not others:

• Go to My Account:

  • Click to UNCHECK the boxes on the request next to the books you CANNOT send.
  • Then click or . 
  • ONLY the books you have left checked will be accepted; the others will be declined

• If you have already accepted the request:

• Go to My Account and click on the transaction for the book.

  • You can do this up until the time you have marked the book mailed.

Pattie, it happened to me before that someone requested a book from a popular author and was very disappointed to see it´s in german. That why I like asking in such cases before sending a book.

June, if I understand correctly, I would have to split the order and after that I would have the possibility to cancel ?