Please add CJK Fonts like "Source Han Sans CJK", "Source Han Serif CJK", "Wenquanyi Micro Hei", "Wenquanyi ZenHei", "Droid Sans Fallback" to LibreOffice Online Docker Image, thank you!
Andras Timar committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/online/commit/?id=0b35934dc168834ed82ab6fa7ae5fe6f3d15ae0d tdf#117557 Add CJK Fonts to LibreOffice Online Docker Image