Hi davidfor!
Thank you very much for your reply and pointing me the font naming issue. I read the thread you suggested (
https://www.mobileread.com/forums/sh...d.php?t=204363), and tried Charis SIL, Times New Roman, and Code2000 (according to this thread
https://www.mobileread.com/forums/sh...d.php?t=108113) but no success at all.
However, I did notice some posts mentioned the firmware issue. I reset my Kobo Wifi to factory mode soon after I got it and the firmware is 1.9. This may be the reason why embedded Chinese epub worked in the thread (
https://www.mobileread.com/forums/sh...d.php?t=184035), but not mine.
Since I read this thread (
https://www.mobileread.com/forums/sh...d.php?t=230567) and others complained about firmware upgrade problem, I decided not to upgrade. Therefore, I am unable to test my hypothesis about outdated firmware prevents embedded Chinese fonts from displaying. At least my Kobo Wifi works just fine in English epubs. I have spent too much time trying to dig out possible causes, and I think this may be the time to stop.
Thank you all who read my post and gave me suggestion. I love this forum!