I'm not sure about this....
Is J-31 really a 'rip-off' of F-35?
I know that there are some minor designs difference, like J-31 having two engines while F-35 has one, but from the outside, the appearance looks pretty similar to each other....
Having different number of different engines alone is a big difference.
But overall, it's a very different aircraft, and technically it's much more of a scaled down f-22. Sometimes to its detriment.
Not terribly ambitious aerodynamically, but same can be said about the non-B f-35 itself. If it works - it works, so there is a string of several - 3 - "twin-engined f-35ski".
(though they're conceptually closer to stealthy hornets in that they're trying to achieve).