The dollar has strengthened sharply in recent months, against Asian currencies in particular. A rising crescendo of apocalyptic financial talk threatens to spook markets. The Japanese yen appears to be on the verge of collapse. China may feel compelled to devalue, with damaging consequences for itself and the global economy. So, can anything be done to head off the dollar’s strength, and even if something can be done, should it?

First the facts. The Japanese yen has fallen dramatically, reaching ¥160 to the dollar at the end of April, down 13% since the start of the year and more than 50% since...