It can work the other way, of course. But at the moment, the U.S. government is printing a lot of dollars, and that pushes up the value of foreign currencies from places where this kind of currency inflation doesn't exist.
Mathias echoes the recommendation of investing in actively managed mutual funds. He thinks most U.S. investors are wise to shy away from ETFs based on foreign stocks and indexes. They are too confusing and too risky, he says. "It's like playing a lottery game with your money."
If you're knowledgeable about world economies, the next step for international investors in search of yield is bonds in emerging markets issued in the country's currency, also known as sovereign bonds. The returns on these can be very attractive. "Sovereign bonds are in much better shape than those issued by the developed world," says Martin.
He sees what he calls "classic corruption" and heavy-handed crackdowns on unrest in China, and "rocky politics" in Mexico, Argentina and Brazil, which affect the economic picture. But overall, "The upside is fantastic. It's worth taking some risk," he says.
He urges investors in sovereign bonds to stick to investment grade and limit their purchases to bonds with maturities between four and five years. "Be well-diversified and liquid."
Aaron Katsman, a financial adviser with Portfolio Resources Group, is another enthusiastic emerging-markets bond investor. An American who is based in Israel, Katsman has clients worldwide. "American investors have done very well with foreign bonds," he says. "You can invest directly or through managed funds or ETFs. They have substantially higher dividends -- north of 5 percent."
Mathias is a little more cautious. He tells investors that if they want to buy foreign bonds or individual foreign stocks, they should identify "a money manager who has a very good track record in these markets."
"There is just a lot of risk," he warns. "The faster the foreign country is growing, the greater the risk. It's much easier to buy than it is to sell. You just don't have the protections that you have in the U.S."