There is an option to use other dictionaries than English. Go to Preferences > Spell Checking > Correction. There are buttons for »New Dictionary« to create a new dictionary, and »Add« to add an existing one.
After creating a new, empty dictionary, you could copy and paste a Swedish word list into a new Papyrus document and add all the words to the Swedish dictionary. However, I don’t know how to add all the word at once (there used to be an option for that but it seems to be gone).