South Korea’s ballooning current account surplus over the past year has landed it on the Treasury Department’s currency monitoring list, the only addition the agency made in its latest semiannual report on to Congress on the macroeconomic and foreign exchange policies of major trading partners. Treasury assesses whether countries belong on the watch list based on three criteria: a bilateral trade surplus with the U.S. of at least $15 billion; a material account surplus of at least 3 percent of...