Does the failure of a buyer of goods to object to allegedly non-conforming goods constitute an acceptance under Pakistani law?

Yes. If, upon delivery of the goods, the buyer finds any deficiencies or defects yet fails to inform the supplier/seller, either at the time of delivery or within a reasonable time period, it would constitute acceptance.   

Section 42 of the Sale of Goods Act, 1930, is pertinent in this regard and it provides as follows:

“The buyer is deemed to have accepted the goods when he intimates to the seller, that he has accepted them, or when the goods have been delivered to him and he does any act in relation to them which is inconsistent with the ownership of the seller, or when, after the lapse of a reasonable time he retains the goods without intimating to the seller that he has rejected them.”