TOKYO (Reuters) - Asian shares were mostly weak on Wednesday with investors cautious after U.S. President Donald Trump tempered optimism over progress made so far in trade talks between the world's two largest economic powers. MSCI's broadest index of Asia-Pacific shares outside Japan was down 0.2 percent, while Japan's Nikkei lost as much as 1.4 percent to hit a 1-1/2-week low and the Shanghai Composite Index retreated 0.6 percent.