Many people speak English and some Russian.
The money is the Afghani and the black market is the only real place you can exchange notes. Figure on a U.S. dollar getting you 44,360 afghanis. Be forewarned that there are two afghanis. One, called Dostum money, is used in the north and is one-tenth of the value of the Talib afghani used in the south. They look identical except for the spacing between the type on the front.