First contact between Europeans (viz. Portuguese) and the Japanese in Japan is said to have taken place in 1543, and Jesuit missionaries began visiting Japan only a few years later. One of the first missionaries was Francis Xavier, who had met a fugitive Japanese man named Anjiro in Malacca. Anjiro accompanied Xavier to Japan and acted as a translator and guide. I have no idea whether he was 'the first' person per se, but I wouldn't be surprised if Japanese abroad had had earlier interactions with European traders and learned to speak their language.

The first Japanese person known to have visited Europe was Bernardo the Japanese, one of Francis Xavier's first Japanese disciples, who came to Portugal in 1553 and thereafter visited Spain and Italy.