Hey all. I share my PRS-505 with my wife, who reads Chinese books. I've never been happy with the english characters in the Chinese fonts though, so I merged a couple fonts into one. The english glyphs come from Bitstream Vera Serif, which I think is easier to read than the stock Dutch. The Chinese glyphs come from FangSong, which my wife says is the most readable Simplified font. The fixed-width latin glyphs (commonly used in Chinese text) are copies of the base Vera Serif glyphs, but bumped out to fixed-width.
It's big, around 15mb. I convert everything to ePubs and use the css trick to point to this font which I put in the /fonts directory. There are instructions elsewhere on how to do this - I could just never find a worthwhile font to do it with!
Please - this is the first time I've ever even looked inside a font, so if I did something horribly wrong or missed something, let me know.