As it turns out, learning Japanese is not that hard

One of my main arguments is that thanks to Brother Juan's linguistic ability, St. Francis Xavier was able to be much more effective than he might otherwise had been.

A brief background on Xavier's Plan A for Japan was that a native Japanese convert to Christianity was act as his interpreter.  Anjiro was of the Samurai class and on the run for murder in his home town of Kagoshima on the southern tip of Japan. Over come with guilt for his crimes, he sought out Xavier in the port city of Malacca in what is now Malaysia.  It didn't work out once back in Japan but fortunately Brother Juan had amazing language skills.

There are several reasons for this: first he was young, barely 23 years old by the time he arrived in India and by that time he was already fluent in three languages, his native Spanish, Portuguese while living in Lisbon, and Latin which was the language of the Church which he undoubtedly learned in the seminary.

As for the Japanese language, I quote the Japanese teacher and interpreter Namiko Abe where she says, "If looked at from a linguistic point of view, Japanese is considered one of the easier languages for a beginner to learn.  It has a simple pronunciation scheme and with few exceptions a straight forward set of grammatical rules.  Limitations on sentence structure are also quite minimal.  The most difficult aspect of learning Japanese is the mastery of reading and writing of Kanji."  Thus it is doable especially if one has linguistic talent.

In a relatively short period of time in Europe, Brother Juan had to learn Portuguese and get up to speed on Latin.  Clearly, whether he was aware of it or not, he must have had a personal strategy for learning new languages.  Obviously he was successful at it, so he must have possessed incredible talent as well.

What Brother Juan was able to accomplish speaking Japanese is amazing; street preaching in 16th century Japanese cities where he gave commentary on Gospel readings; acting as Xavier's interpreter in disputations with Buddhist priests, and in the courts of Japanese warlords, also interpreting for Xavier, giving the latest European scientific knowledge on geography, astronomy and climatology. The Japanese were amazed with Xavier's wisdom and knowledge all possible thanks to Brother Juan's language skills.