Anglo-Norman language
It is believed that Fantosme was an Italian (named "Giordano Fantasma") who came to England in the train of Henry of Blois. A few lines from his poem suggests that he was Scoto-Norman, but this may have been inserted for the sake of the minstrels who would be reciting the piece. On the other hand, Fantosme may have simply identified with his adopted country, he referred to messengers of William, who were also subjects of the Young King, as "noz" (ours). Considering his evident knowledge and skill in the Anglo-Norman language, the most likely hypothesis is that he was Anglo-Norman.