A classic language barrier incident caused a B747-400 flight crew to climb to 7;900 meters vice 7;800 as corrected by ATC.

Narrative

Due to bad weather and traffic congestion we departed 3 hours and 33 minutes late due to Shanghai ATC delays. Once airborne I noticed immediately that ATC was extremely saturated and that the Chinese pilots were speaking almost exclusively in Chinese and radio courtesy was non existent. On the climb out we received a climb to what I thought I heard as 7;900 meters and I responded back to Departure the same. We leveled at 7;900 meters (25;900 FT) several minutes later ATC called us to verify level at 7;800 meters. I responded that we had leveled at 7;900 meters and they directed us to descend to 7;800 meters (25;600 FT). We continued on at 7;800 meters until the next level change and the rest of the flight was uneventful. The mix up on the altitude came from radio congestion and possibly poor radio transmission quality from ATC. My First Officer and I briefed about the difficulty understanding the controllers and this was a perfect example. Obviously they have a hard time understanding us as they did not pickup on my repeating 7;900 meters VS 7;800 meters. Due vigilance on communications is key in all places where English isn't the primary language.