I trade mostly trade with EURUSD, USDCAD.
Currency risk can be reduced by hedging, which offsets currency fluctuations. If a U.S. investor holds stocks in Canada, for example, the realized return is affected by both the change in stock prices and the change in the value of the Canadian dollar against the U.S. dollar. If a 15% return on Canadian stocks is realized and the Canadian dollar depreciates 15% against the U.S. dollar, the investor breaks even, minus associated trading costs.
I also mainly use standard currency pairs, which are very popular.