In the application kit [Appendix A checklist], there is a clear instruction
for this.
"If your documents are not in English or French, send a notarized/certified translation with a copy of the originals".
Thus for both Hukou and Marriage, just
send notarized documents.
Actually for many seniors who may not keep their original marriage certificates, they
just need to get a notarized marriage
relationship with their photo but without a photocopy of the original and it is fine.