@Kovid,
This is related to Bug Ticket #5982 on Calibre generated chinese news EPUB. I am not sure how hard it is to fix, but I tested again and confirmed that the garbled Chinese display of the article description line on the Feed page ( UTF-8 encoded feed) can be fixed by simply removing the line "Font-Family: SANS" under ".articledescription" of the stylesheet.css.
Can you please take a look?