I’m using en_US.UTF8 as my default locale, and have pretty much every locale known to man enabled at the moment (locale -a shows a rather huge list, including the relevant Chinese locales) and I have fonts installed which I know can display the appropriate characters; they show up with fc-list without any problem.
I’m using jodconverter to convert RTF->PDF, and when I do so, the PDFs have lots of little squares instead of Chinese characters. The PDFs don’t have any Chinese fonts embedded, and I have no idea how to determine why.