Three consecutive patriarchs of Esoteric Buddhism were Amoghavajra of India, Huiguo of China, and Kūkai of Japan. This paper foregrounds the usually taken-for-granted but vital historical role of language education and translation in the international spread of religion and culture. There had to be sufficiently educated bilingual or multilingual priests to translate Buddhist scriptures and to travel internationally before the golden age of East Asia could be realized, with Emperors in T’ang Dynasty China and Heian Period Japan welcoming foreign representatives and patronizing Buddhism. Japan’s great saint Kūkai was educated in Chinese and Sanskrit, thus able to contribute to Sino-Japanese relations as well as to systematize Buddhism and other Asian religions. This paper analyzes a biography of Kūkai that also illustrates the issue of voice in translations. A translated work ideally speaks with one voice, that of the original source, with the translator remaining invisible. Yet in this case, the Japanese-English translator has a distinct writing style in her second language, while the biographer alternates between a flowery classical Chinese rhetorical style and blunt intrusions into the story, which in turn reflect the ambivalence in quotations from Kūkai. Disparate voices can therefore be discerned along with the linguistic and cultural issues involved in a Sanskrit-Chinese-Japanese-English chain of communication.