Bro, one of the easiest way is to go to a local BAR on the first night of your stay in Vietnam. If you go to a bar patronised by foreigners, there's a high chance that the girl you get for the night will know some english. Take her phone number and make an appointment for the girl to bring you around the next day. Its that simple
If you come to HCM, a good place to try is CatWalk at New World Hotel. The price is higher but the probability of the girl speaking mandarin or english is high. As for Hanoi, try Fortuna Hotel's KTV, BOSS.
Happy Bonking