(Reuters) -- The yen fell on Wednesday to its weakest levels against the dollar since 1990, with markets alert to any signs of intervention from the Japanese authorities to prop up their currency.The dollar reached as high as 155.17 yen, its strongest since 1990, before falling back in choppy trading, a sign of market nervousness around the 155 level. It was last at 154.97, up 0.09%.The decline in the yen comes after a string of strong U.S. inflation data pushed the dollar to five-month highs and reinforced expectations that the...