A biography of Giuseppe Caspar Mezzofanti was written in 1858.
In a chapter starting on page 457, Russell attempts to skeptically evaluate the claims.
He finds several challenges including:
- How many words do you need to know in order to claim knowledge of a language?
- When are two dialects considered two languages?
- All the reports were indirect. Mezzofanti did not produce a list himself, as he planned, before his death. (i.e. someone said that he said in 1846 that he knew 78 languages, his nephew computed 114 by going through his papers.)
Russell lists some 94 "languages" produced from a list made by Mezzofanti's nephew. He also lists 30 languages that Mezzofanti was "frequently tested and spoken with rare excellence".
I don't think I can sum up the evidence and the difficulty of counting the languages spoken by an historical figure (given only second-hand reports, no clear definition of fluency and no clear definition of where one language stops and another begins) any better than Russell himself:
Summing up, therefore, all the authentic accounts
of him as yet made public ; discarding the loose
statements of superficial marvel-mongers, and divesting the genuine reports, as far as possible, of
the vagueness by which many of them have been
characterized, it appears that, in addition to a
large number of (more than thirty) minor dialects,
Mezzofanti was acquainted in various degrees with
seventy-two languages, popularly, if not scientifically,
regarded as distinct :— almost the exact number which
F. Bresciani ascribes to him ; that of these he spoke
with freedom, and with a purity of accent, of vocabulary, and of idiom, rarely attained by foreigners, no fewer than thirty ; that he was intimately acquainted with all the leading dialects of these
that he spoke less perfectly, (or rather is not shown
to have possessed the same mastery of) nine others,
in all of which, however, his pronunciation, at least,
is described as quite perfect; that he could, (and occasionally did,) converse in eleven other languages,
but with what degree of accuracy it is difficult to
say ; that he could at least initiate a conversation,
and exchange certain conversational forms in eight
others ; and that he had studied the structure and
the elementary vocabularies of fourteen others. As
regards the languages included in the latter categories, it is quite possible that he may also have spoken
in a certain way some at least among them. So far
as I have learned, there is no evidence that he
actually did speak any of them : but with him there
was little perceptible interval between knowledge of
the elementary structure and vocabulary of a language, and the power of conversing in it.