This issue burned a few hours of troubleshooting and I wanted to share it here for posterity.
If you're trying to generate a PDF from HTML that contains Chinese (or Japanese, etc) characters AND you're using some type of non-standard web font in your CSS you might run into an issue where the ideograms get rendered as squared x's.
If you see this issue you need to use one of the standard web safe fonts such as Helvetica, Arial. We were forced to go from:
font-family: MuseoSans, Helvetica, Arial, sans-serif;
font-family: Helvetica, Arial, sans-serif;