Those top-rated Chinese researchers are publishing in English. Their Chinese-only venues are not at the caliber that they would consider publishing ground breaking work to.
The *ACL conferences (major NLP venues) decided to allow presentations to be in Mandarin now; the rationale being that a lot of presentations were in such poor English already, might as well let half the audience be engaged.
It will take at least a few more years before submissions are allowed in Chinese: reviewers can't be assumed to know Chinese. The momentum is there though.
Of course, but especially in the applied sector of ML, it can happen that interesting blog posts and code examples are increasingly written in Mandarin.
