The "taro" spelling comes from Tahitian which is a closely related language to Hawaiian, but uses t where Hawaiian has k and r where Hawaiian has l. Though taro is eaten throughout Asia, it didn't become a European thing until they found the Tahitians eating it. Even in Hawai'i, when it is discussed in English (at least in tourist areas) it is usually called taro instead of using the native version of the word (kalo). By the way, in most dialects of Spanish it is called malanga.