When the average kinetic energy of the molecules goes up (a rise in temperature), the average speed of the molecules increases. And lower average kinetic energy of the molecules means they have lower speed. However, a change in average kinetic energy is not directly proportional to a change in average speed. 1.
An appreciation means an increase in the value of a currency. It means a currency is worth more in terms of foreign currency.
1 Your goal, then, is to exchange currency when your currency is high and the foreign currency is low, because this means that you'll get more of the foreign money than you would otherwise.  Understand that the dollar (for example) being worth less than the euro doesn't have much to do with the cost of items.