FDM for Android always trend to use single font for CJK text, which caused weird display for some users.

Chinese (China):


Chinese (Taiwan):


Japanese:


Korean:


Noto Sans CJK is shipped in most Android devices for interface, and the font provides different variants for Chinese (China), Chinese (Hong Kong), Chinese (Taiwan), Japanese, Korean, it's reasonable to make use of them for different locales respectively.

See a discussion with the same problem on an Android app at GitHub: https://github.com/mozilla-mobile/fenix/issues/13863