TextEdit always displays in an Asian font.

Whenever I try to open a document with TextEdit that's been created on a different computer, or downloaded, it displays with an Asian font. (My guess is Japanese.)

So, for example, if I create a document in TextEdit on my work computer and save it on Dropbox, when I get to this computer and open the document, it opens up with all of the text in Japanese. If I drag the document to Word and open it there, it opens and is in English and is just fine -- but I don't understand why it's opening ALL TextEdit documents using the wrong font. This happens with readme files downloaded from online, too. I just can't open documents with TextEdit!

I've checked what font is default, and it's Monaco and Helvetica.

Does anyone have any ideas about what's causing this and how to fix it? I'm running 10.6.8 on a 3.06 GHz Intel Core Duo iMac.