For writer and translator Polly Barton, you’ll find “the beating heart of Japanese” in onomatopoeia, mimetic language that sounds like what the words signify. Bow-wow. Woof-woof. ワンワン. (Wan-wan, rhymes with “bonbon.”) Japanese has a massive onomatopoeic vocabulary second only to Korean, claims Barton, who set out to master this essential aspect of the language: “I …