But basically there is no such thing like "chinese keyboard" -- what you get is usually the international english keyboard, whether it is different from the british keyboard I have no idea. The warranty is probably valid globally, though it is safer if your friend ask for you personally. You will definitely nee a power adapter because the chinese plug is something like the american one.
However, the price of apple machines in mainland china seems to be not attractive at all, at least when compared with the euro price in france (the place where I am now), which is by itself high. You may get taxfree when your friend exit China with the machine.
But alternatively, HongKong would be a perfect place to buy the laptop, where you can get the lowest price, the best-fitted power adaptor and the warranty, I think.