The plaintiff would not be invoking any international law. Individuals working for the Chinese government stole computer secrets from U.S companies, stored in computers on U.S. soil. That's covered by U.S. and state civil and criminal laws. If they prove their case, and a judgement is awarded, China has to pay up. If they don't pay up, then a judge sends a sheriff or a marshal to seize property. Here's a random link about a lawsuit against Iran and Syria http://usnews.nbcnews.com/_news/2012/05/16/11733643-family-w....

'Wultz Attorney Robert Tolchin told msnbc.com that with the court judgment in hand his clients can seek Iranian and Syrian assets to collect the award. Tolchin said he couldn’t be specific, but he would explore “various avenues.” “There is a lot of litigation by people seeking the turnover of Iranian assets,” Tolchin said. “The Iranians have kept U.S. courts busy.”'

At which point China kicks the US company out of China, and said company loses far, far more than any amount that is due to hacking.

Iran and Syria aren't subject to this problem because the amount of business that US companies do in Iran and Syria is trivial.

Possibility: A suit under the Alien Tort Statute: https://en.wikipedia.org/wiki/Alien_Tort_Statute