Having listened to the entirety of the ATC tape, I see no problem whatsoever with their English. Two voices on the radio, probably the Captain at first and then the FO. The FO English was slightly better; but both were very good (definitely better than ICAO 4 - I have heard ICAO 4 speakers). Their English is better than, for example, the rapid-fire accented "English" that you can hear at US airports - I have great difficulty sometimes understanding US ATC. I suspect the main difficulty for the crew in this case was in handling a difficult emergency.
The Aussie ATC was good, she spoke slightly slower and enunciated clearly.
FYI, all Chinese learn English at school and have done so for 20? or 30? odd years. The Captain on this flight was very experienced and senior, I think in charge of the flight simulators. There was no expat Captain on board.
Listening to the progress of the emergency, firstly engine at idle, then consideration of burning off fuel, then visual inspection, then decision to return overweight rather than wait - it all seems logical and measured. A good job, I think. I'd rather think better of a fellow professional than go off on imaginary tangents speculating on things that we don't know.
Oh, and it's "fault". I think many Asian speakers have difficulty with the English "L" sound, making it closer to an "R" sound. Funny responses on this thread, though.