The pay in China is after Chinese tax is paid, at least if the airline doesn't cheat. I got an official tax certificate showing how much they paid the government.

Chinese (and Japanese) taxes are higher than in the US. Because of this, if you understand our tax code, you get "foreign tax credits" to count against future tax liabilities up to ten years in the future.

In my case, because of the time frame that I worked in China, i will get somewhere around 30k USD in tax credits for the last 18 months I worked in China.

I believe Skymark in Japan also pays Japanese tax. If they do it legit, same deal. You should end up owing nothing in US tax for your Japanese income, and earn foreign tax credits for your future US tax liabilities.