Are international PhD students offered Teaching Assistant (TA) positions during their research programme in China?
tl;dr: It strongly depends on the relative perceived status of where you are coming from vs. where you're working at. If you're from a top-300 university (especially from the US) taking your PhD at a mid-tier Chinese university, you're likely to get offers. If you're from a low-status country/department in a large institution, expect empty promises.
I have accepted a postdoctoral contract in a mid-tier Chinese university, which was not a pleasant experience. One of the main conditions by which I accepted their postdoc offer was precisely a declared prospect of ultimately hired getting as a TA. Eventually I've learnt from other postdoc colleagues that they were all told the same story, but only the first foreign PhD that ever came from abroad got hired. Others worked hard towards pleasing local staff until they would burn out and leave. First they're told they can get a TA offer if they publish many papers, then if they publish higher impact, and after achieving that, if they can earn a top competitive grant. I've a friend who just went through all steps involving >20 papers and 2 big grants, and all he got out of it was a 6-month agreement to teach a single topic in exchange for a low pay.
We are all postdocs coming from 3rd world countries. I eventually met an English professor who got hired straight away from abroad. I've also heard from European and American colleagues from other institutions in China who had no trouble getting local contracts. I have nonetheless met dozens of Pakistani, Middle-Eastern, Indian fellows who were jumping from one institution to other without getting ever getting anything solid.
Chinese culture is strongly conscious over status. Abiding to very local standards. My general advice is, if you're not a US-passport holder neither coming from some US university, if you're not caucasian fully-fluent speaker of English, if you haven't published in top-prestige journals, or at least not from some top-300 [national rank] university or 1st-world citizen, don't nurture high hopes of being offered a staff position in China. And beware of empty promises.