while I can't help you with Air China, I don't think that the 2nd bag surcharge is a hidden fee. Maybe the taxes on your ticket (or exactly what you pay in taxes) are hidden, but they certainly have announced all the other charges like the 2nd bag charge

I flew Air China last year with no "hidden fees". New Checked Baggage Policy on Routes between the US and China: General Rules Economy Class Baggage Allowance • Two bags per passenger may be checked free of charge • Maximum dimensions of each piece should not exceed 158cm (62 inches) • Maximum dimensions of two pieces should not exceed 273cm (107 inches) • Weight allowance for each piece is 23kg (50 lbs) Business and First Class Baggage Allowance • Two bags per passenger may be checked free of charge • Maximum dimensions of each piece should not exceed 158cm (62 inches) • Weight allowance for each piece is 32kg (70 lbs) As a Platinum Member, you’re entitled to more baggage allowance: • On routes where the weight of baggage counts, a Platinum Member is entitled to 30 kg worth of free baggage allowance above the normal, irregardless of which class your ticket is in; • On routes (e.g. China-US, China-Canada) where the number of pieces of baggage counts, a Platinum Member is entitled to 1 more piece of checked-in baggage above the normal, and the limitations on the weight of baggage are as follows: 32 kg for the First Class and Business Class and 23 kg for the Economy Class, and the sum of the length, width and height mustn’t exceed 158 centimeters.