Hi Hinrich,
It's possible to ride a foreign plated bike into China, and while not impossible, getting to do so is not particularly easy.
First steps involve arranging a 'Carnet de passage' or simply referred to as a Carnet, basically a bonded amount of money held by an approved organisation (usually a auto-mobile club/association). that then issue you a Carnet document which has to be presented in those borders that accept them.
For Ch!na, you need to arrange and pay for a government APPROVED guide who will navigate with you for the entire route inside mainland Ch!na, the guide uses their own vehicle - where you go, the guide goes. This is a substantial cost, as you pay for that persons time, per day plus all their lodgings etc. You have to submit a ruote plan which needs approval, and it is expected that you stick to the route and schedule. Arrangements have to be made for you to get a temporary Ch!inese issued drivers licence, as IDP (international driving permit) are not valid in Ch!na. Sometimes temporary licence plates are issued which have to be attached to the vehicle/bike for use on roads here. Also a vehicle coming into Ch!na can only venture here by prior arrangement and only for a very limited duration.
There some threads on MCM here about other who have thought, attempted, failed to do a ride inside the middle kingdOm, but some have been successful.
If you need some information I can dig up some contact details with a couple agents who deal with this, but a warning it can be a fairly expensive exercise...
The bike has to exported/transported back out of the country, otherwise you forfeit your bond (Carnet).
You might find some of the other riders who intended to do something similar as yourself in this
trip planning and making tracks thread, or check other motorcycle forums e.g. ADVrider, GT-Rider etc.
Personally, I'd recommend riding other places e.g. Thailand, than here, as Ch!na is not particularly motorcycle friendly especially for someone who has never ridden here before, though that can depend on previous experience and intended route.