Why is building a high speed railway infrastucture anything special? My understanding is that the track and OHC will be pretty standard (correct me if I'm wrong), and with earthworks and bridges we seem to have no problem doing those for motorways. The route itself has already been "designed". IDK about signalling, but are we likely to adopt Chinese standards for that? the ORR would have a fit. The trains are a different matter, but I doubt that it would be politically acceptable to build them in China, even if they were a Chinese design.
The only thing the Chinese might bring to the party is project management, but that will only work well if they can use the authoritarian approach which is cultural norm in China itself.