Senior monetary officials usually talk in code. So when Ben Bernanke, the Federal Reserve chairman, spoke recently about Asia, international imbalances and the financial crisis, he didn’t specifically criticize China’s outrageous currency policy.

But he didn’t have to: everyone got the subtext. China’s bad behavior is posing a growing threat to the rest of the world economy. The only question now is what the world  and, in particular, the United States  will do about it.

Some background: The value of China’s currency, unlike, say, the value of the British pound, isn’t determined by supply and demand. Instead, Chinese authorities enforced that target by buying or selling their currency in the foreign exchange market  a policy made possible by restrictions on the ability of private investors to move their money either into or out of the country.

There’s nothing necessarily wrong with such a policy, especially in a still poor country whose financial system might all too easily be destabilized by volatile flows of hot money. In fact, the system served China well during the Asian financial crisis of the late 1990s. The crucial question, however, is whether the target value of the yuan is reasonable.