Gottfried Wilhelm Leibniz was a German polymath. I've found information that says he was a polyglot who wrote primarily in Latin, French and German, but I cannot find any specific info about the other languages he spoke or wrote in.
Among his other accomplishments, Leibniz was one of the pioneers of what we today call Linguistics. This means he studied a lot of languages, but would have had a smaller set he actually was good enough to communicate in. Given this spectrum of competency, it would probably be best to classify languages he "knew" by how he used them.
Languages he actually wrote in:
- Latin (most of his work)
- French (A lot of his philosophical work)
- German (his family journal. Almost certainly his native tongue)
- English (some essays on Hebrew)
Languages he likely knew and/or proclaimed expertise in
- Classical Chinese (He wrote extensively about it)
- Hebrew (Correctly refuted the idea that it was the original language of humankind)
- "Slavic Languages"
Languages he had some exposure to:
- Classical Greek
Languages he's reported to have known in some way, but I so far haven't been able to track down reliable references for.
This post is intended as a 'supplement' to T.E.D.'s, filling in some details on when and how he learnt various languages.
Until the age of six, when his father died, Leibniz spoke German at home. At seven he began to teach himself Latin using illustration and a work by Livy to help him. At either nine or twelve (depending on which source you believe), he started teaching himself Greek (classical rather than modern), though by this time he was already at a school where pupils were only allowed to speak Latin and Greek. Later, he read Aristotle in Greek. He also wrote and recited poems in Latin as a child, and continued to do so for the rest of his life.
At the University of Leipzig,
Among the other topics which were included in this two year general degree course were rhetoric, Latin, Greek and Hebrew.
According to Kato Lomb (herself a polyglot) in Harmony of Babel, Leibniz
wrote his doctoral dissertation in Latin, his historical treatises in English, and his books on theology in French. He agitated in German for rapprochement toward France.
Throughout his life, most of Leibniz's correspondence (he had hundreds of correspondents) was written in Latin and French, with a small amount in German. On German,
Leibniz, unlike many of his contemporaries, wrote German clearly and well, and he considered its mastery essential to the progress of modern European society....it is ironic that his work arguing for the use of the German language was in fact written in Latin.
He polished his French during his time in Paris, before he went to work for Duke Johann Friedrich (of Brunswick - Lüneburg - Calenberg) as Privy Counsellor at a court where the language was French.
Leibniz spent quite some time in England, meeting many people there, so it is not unlikely that he also spoke English at least reasonably well. He also spent over a year in Italy, his knowledge of Italian demonstrated by this story which he liked to tell:
There is a story from that period, which Leibniz was fond of repeating. While he was crossing alone in a small boat from Venice to Mesola in Ferrara, a violent storm blew up. The ship's pilot proposed to throw Leibniz overboard and keep his possessions and money. As justification, the Italian pilot asserted (since he did not believe he would be understood by Leibniz, a German) that he considered him the cause of the storm because he was a heretic. Whereupon Leibniz brought out a rosary he had taken with him as a precaution and pretended to use it devoutly. This artifice succeeded; a sailor told the pilot that since Leibniz was not a heretic, it would not be right to throw him overboard.
For many years, Leibniz communicated (in Latin) with Jesuits priests in China as he was deeply interested in Chinese thought, culture and language, all three of which he devoted a considerable amount of study time to. In addition this, as a linguist with a particular interest in constructing an artificial language, Leibniz studied a variety of languages, including Welsh, Danish and Sanskrit (but there is no firm evidence that wrote in or spoke any of these).
Benson Mates – The Philosophy of Leibniz