What is a good way of getting peer feedback on my draft cover letter?
The most German universities have career service departments for questions like this. If this is uncommon in Sweden, I agree with Kimballs comment: show it to people you trust.

In addition: the Internet is full of resources like guides and tips. Just be aware of possible cultural differences that may appear between countries. A guide targeting to US audience could suggest or advice elements that could count as "no gos" in other cultures. If you want to check your cover letter against some online guide I suggest you to search one in Swedish that considers the national or cultural specialties.