Japan’s international trade activity dropped 10.4% year over year in August after a 1.4% slip in July. That’s included an 8.2% slide in global exports and weakens the Japanese government’s leverage just as the closure of a restricted trade deal between the U.S. and Japan is due to be signed by Prime Minister Abe and President Trump on Sept. 25. Exports to the U.S. fell 4.4%, including a 13.0% drop in shipments of autos where the future of tariffs remains uncertain. Looking globally, Japan’s export downturn was widespread with all but one of the 18 sectors track...