Upon arriving in Japan in 1549 to convert the natives to Christianity, it is not surprising that St. Francis Xavier ran into communication difficulties. While he was positive overall about the Japanese people, he came up with a remarkable theory about their language. He found communication so challenging that he wrote of his belief that the Japanese language had been planted by the Devil in order to stymie Christian missionary work.
A country of devil-tongued natives? I wonder what embarrassing communication mishap was preying on his mind the day he wrote that letter?
There are plenty of candidates for the element of Japanese study that could have driven St. Francis over the edge: kanji; the lack of a grammatical subject; kanji; the special humble and polite forms of address; more kanji; the lack of clear differentiation between present and future tense; and even more kanji.