Chinese airlines, like so many in other Asian countries, expect you to stay with the company for your whole working life. For Chinese nationals, mobility of labour is virtually unknown. The airlines are not in the business of teaching you to fly for another company so you effectively have a lifetime bond. This works both ways, they have you for life and you have a job for life. There are also lots of invisible perks, assistance with house purchase, medical treatment for your family etc. In extremis if you lose you medical for any reason they will continue to employ you at something like 70%-80% salary until retirement and then pay you a pension. Should you not relish the thought of sitting around doing nothing for twenty-odd years then you can leave because you are not flying for another airline.
As far as T&Cs are concerned there is a level playing field because they would run out of recruits if there wasn’t. There is also an element of moonlighting. I know of one China Southern pilot who took a weeks leave, flew for another airline, pocketed RMB10,000 and then went back to work.
The same criterion does not apply to foreign pilots. You are already trained and are on fixed term contracts. The only problem starts if you try to leave before the end of your contract for the simple reason that they have had the expense of obtaining your Chinese licence plus all your company OPCs. If a company wants you to pay these costs in advance then close the door behind you.
Except for a few start-ups all the F/Os are Chinese. An English comprehension test is required for their licence and as English has been taught in all Chinese high schools for the last fifteen years the standard is quite high. This is helped by the large number of native English speaking teachers in China who teach English as opposed to Chinglish.
There is a different way of doing things in China that has been established over the last three thousand years. You cannot impose your rules so you have to accept theirs. It can be frustrating or downright bloody unfair, but you cannot change it. If you don’t think you can cope with it, don’t come.