I think it has to do with how special characters are written in code

For instance, I found that the dash character (-) appears as & #045; on my feeds.

A little scripting can replace common coding errors like that with the actual characters

If I know which widget you're using I could crack it open and see if the problem can be fixed in the script. Also what's the url for the site are you trying to get feeds from?

I had a look at the widget and the sites. To my understanding some feeds are formatted to handle foreign characters and symbols, others aren't. If you take a look at the script for the widget you'll find a series of code that look like this:

rssdata = Replace(rssdata, "'", "'")

This is where you would replace the gibberish with the correct characters.
Unfortunately there's no way to type squares, and even if you could there would be no way to tell if that square is actually an ä, ö, or an ë. Sorry, I don't see any solution here. Keep asking around though, maybe some more experienced coders around Stardock/WinCustiomize can help you out.