First, check the list of noto fonts for the language that you want and download it to your computer. https://www.google.com/get/noto/

I used: 
Japanese: https://fonts.google.com/noto/specimen/Noto+Sans+JP
Chinese: https://fonts.google.com/noto/specimen/Noto+Sans+SC
Chinese (Traditional): http://fonts.google.com/noto/specimen/Noto+Sans+TC

Go to System > Storage > then connect your device to your computer, and toggle “USB web interface” to on.

Enable Developer Mode on your Remarkable paper pro (Go to General > Software > Advanced > Developer Mode > Enable)

Note!!! It will earse all data on your Tablet.

Then open a new browser and connect to your device with the URL supplied after turning on the USB interface. 10.11.99.1

Open an SCP tool like WinSCP. https://winscp.net/eng/download.php

For WinSCP as follows:

File Protocal: SCP / Host: 10.11.99.1 / User: root / Password: find it at the bottom of Help > Copyrights and Licenses > GPLv3 Compliance. Your password is here. Port: 22

Go To Front Path: /usr/share/fonts/ttf/ for the Remote Site address.

The ttf font file folder will open. Create a new folder called “opentype” under ttf.

Drag the fonts that you downloaded and extracted into the new folder.

Files I uploaded:

NotoSansJP-VariableFont_wght.ttf
NotoSansSC-VariableFont_wght.ttf
NotoSansTC-VariableFont_wght.ttf

Then Reboot, done.

!!!Note: If you received the warning about NO PERMISSION to write, please follow the instruction below.

Use Putty login the tablet via SSH
Run the command below:

mount -o remount,rw /