Voltaire was quoted often in the past week: "I disapprove of what you say, but I will defend to the death your right to say it." But Voltaire never said that, as can be read in the "misattributed" section of the Wikiquote page on Voltaire.
Still, at least the quotation is from one person's attempt to sum up Voltaire's position on free speech. The same cannot be said of another Voltaire attribution that just crossed my path: "To learn who rules over you, simply find out who you are not allowed to criticize." This turns out to be a quotation from an American white supremacist named Kevin Strom (see the Wikiquote page again).
Voltaire did actually say a few things. Here's one of them (found by skimming that Wikiquote page): "Un bon mot ne prouve rien." Or as that page translates it, "A witty saying proves nothing."