Downloading any text at enWS or zhWS (and presumably the other Wikisources) with CJK characters in it causes "boxes of doom" in the PDF export:
This works OK in EPUB and TXT exports:
Example: https://en.wikisource.org/wiki/Domicile_Ordinance
And the PDF produced from https://ws-export.wmcloud.org/?page=Domicile_Ordinance&lang=en&format=pdf:

