Hi DNSB!
Thank you for your reply. I did read a lot about Kobo Wifi doesn't support font folder and it only starts from Kobo Touch and later models in this forum. That's why I took the approach of embedding Chinese font in Chinese epub. Unfortunately, it doesn't work for me either. So my question in the first place was why it worked on other Kobo wifi devices but not mine.
Even being aware of that, I still tried font folder approach anyway. I guess I am just a fan of "exhaustion method" and felt the urge to test all possibilities.
I also found others mentioned they had similar situation in this thread:
https://www.mobileread.com/forums/sh...d.php?t=112427
Thank you for your inputs, not only in this thread but also other threads because I read a lot of your posts during my research on this problem.