Another great polyglot was Sir Richard Francis Burton [1]. Not only did he speak more than 20 languages, but he led an incredible life. Edward Rice wrote a great biography [2] (although I read the earlier edition). Burton himself wrote a great deal as well [3].
[1] https://www.amazon.com/Captain-Sir-Richard-Francis-Burton/dp...
[3] https://en.wikipedia.org/wiki/Richard_Francis_Burton_bibliog...