Many readers may know Polly Barton better as the translator behind Aoko Matsuda’s “Where the Wild Ladies Are,” which won an English PEN award last year; and Kikuko Tsumura’s “There’s No Such Thing as an Easy Job,” released in November 2020. But if her latest individual work, “Fifty Sounds,” is anything to go by, Barton is a writer to be reckoned with in her own right.