Graeme Wood reviews Michael Erard's Babel No More:
Hyperpolyglots argue that what they do is not fluent speaking but instead a sort of mechanical reproduction, a robotic trick rather than a human skill. Hale, an MIT professor who died in 2001, is quoted as disputing the idea that he "spoke" fifty languages, limiting his claim to only three, one of them being the Australian Aboriginal language Warlpiri. He distinguished "saying things" from speaking a language and really understanding it. The ability to pretend to converse in a language, and get by, isn't the same as speaking it fluently.
The most famous hyperpolyglot, Giuseppe Mezzofanti, a nineteenth-century Bolognese cardinal, spoke between thirty and seventy languages:
He spoke them so well, and with such a feather-light foreign accent, according to his Irish biographer, that English visitors mistook him for their countryman Cardinal Charles Acton. (They also said he spoke as if reading from The Spectator.) His ability to learn a language in a matter of days or hours was so devilishly impressive that one suspects Mezzofanti pursued the cardinalate in part to shelter himself from accusations that he had bought the talent from Satan himself.
The Dish 