I did some quick playing around with using a Chinese font. Renaming the font files seemed to allow me to access the font on a Kobo Touch but the text still showed as boxes. I went browsing on Mobileread and found a thread about FeedBooks in Chinese
https://www.mobileread.com/forums/showthread.php?t=27769 which had a file called chinese.epub with the Adobe Song Std font embedded which I downloaded.
I opened the .epub file with 7Zip, extracted the chinese.otf font and took a look at it. Turned out to be an Adobe .otf font file with the font name Adobe Song Std L. Renamed the file to Adobe Song Std L-Regular.otf, copied it to the fonts folder on the KT, opened the LinuxToy epub file with Sigil which promptly removed the font file since it was in the css directory and not the font folder. Copied the resulting 19KB file to the KT, disconnected and opened LinuxToy. Usual blocks until I selected Adobe Song Std as the font and then seemed to look fine. I do not read Chinese so I can't say the correct characters were being used.
If you do try this, could you please give some feedback as to whether this procedure worked for you.
Regards,
David