Hi Anne,
Great question! Unfortunately, it will take some work on your part. You will need to create a custom version of the Finding aid XSLTs, replacing the English labels that are found within them with your Swedish headings instead.
Another user has done this for French, and we have the XSLTs available on the wiki, as well as basic instructions on how you can swap out the English one for another. See:
Hopefully by comparing the English and French ones, you can figure out where you need to make changes.
If you do create a Swedish one and would like to share it with the community, please feel free to send it to me and I'll add it to our wiki!
Good luck!