Leave it to a lazy person to improve the world ever so slightly.
Whenever I have a document with Swedish letters or spaces in the file name, I edit those out before sending it as an attachment or onto an ftp.
Here’s an Automator script that easyfies the process.
Drag the file you want to rename onto the script icon and Bob’s your uncle:
Å → A | Ä → A | Ö → O
å → a | ä → a | ö → o | space → _
It’s so basic that it’s almost embarrassing, but since I’ve been doing this manually I figure someone else might have use for it. Not very efficient app though; it’s half a megabyte for searching and replacing 7 characters…