Download the Font
Download the Noto Serif Simplified Chinese font from Google Fonts.
https://fonts.google.com/selection?query=noto+serif+c
SSH into the Tablet
Connect the Tablet to your computer using cable then enable the USE web interface in the Storage tab. Then go to General->Help->About->Copyrights and licenses. At the bottom of the page, you should see the IP address and the password for SSH.
If you don’t have a USB cable or your computer is in the same local network as remarkable, you may just SSH using the local IP address of your reMarkable.
Upload the font
Extract the zip file you downloaded from Google Fonts and upload all the .ttf files in the static directory of it.
As an example, I create a directory /usr/share/fonts/ttf/notoSC first. Then scp all the files.
scp Downloads/Noto_Serif_SC/static/* [email protected]:/usr/share/fonts/ttf/notoSC
Restart the Device
In order to make it take effect, please restart the tablet.