Engines are the hard part, and most of the tech behind building them (particularly in how to make key components like turbine blades) is a closely-guarded trade

Engines are the hard part, and most of the tech behind building them (particularly in how to make key components like turbine blades) is a closely-guarded trade secret of the companies that know how to do it. That's why this plane uses engines procured from CFM (France), and Mitsubishi's in-development regional jet will have engines from Pratt & Whitney (US). There have also been patent issues around some of the other useful bits (such as blended winglets). Aviation Industry Corporation of China announced a deal with Antonov to revive An-225 production and get the tooling and everything for building them in China, and a lot of speculation there is that the deal is much more about getting the engine tech than the plane itself; even though it's behind current engine technology, just jumping to where engine technology was in the 1980s would be a big boost for China's aviation industry.