CJK characters not visible when reader's font face set to 'Publisher Default'

[zxtom]

I'm new to creating epub documents with asciidoctor and currently trying to generate an epub3 with mixed text in English and Chinese Simplified (scripts set to 'multilingual').

The source file is converted to epub with: asciidoctor-epub3 -D output document.adoc

After uploading the resulting epub to a reader (an app, or Kobo) the CJK text is invisible (blank space). I can make it visible by switching the reader's font face from 'Publisher Default' to one that supports CJK script (e.g. AR UDJingxihei on Kobo), however I'd like a font of my choice (ideally the NotoSans CJK SC) to be embedded in the epub.

Am I missing something in my setup? If it's not natively supported in asciidoctor-epub3, could someone point me in the right direction please, or would it be possible to request an enhancement?

When searching for a solution I came across a FontForge script that prepares a NotoCJK font to work with asciidoctor-epub3 and -pdf (https://gist.github.com/mojavelinux/c74162d44ca77d1a7c25), but I'm struggling to find further information on what to do with the resulting ttf. There is also an old post (2014) to which Dan Allen has contributed so I suspect some work has been done in the past on the support of CJK in EPUB3.

[mojavelinux]

FYI, the updated version of that FontForge script can be found here: https://github.com/asciidoctor/asciidoctor-pdf/tree/master/scripts.