"He knew how to speak Esperanto"
by cm

Flag of Esperanto
Public DomainFlag of Esperanto
 Esperanto was invented in 1887 by the Polish eye specialist Dr Ludovic Lazarus Zamenhof. Phonetic, regular, and with simple rules of grammar and pronunciation, it was intended as a universal second language.  It has never taken off to any significant degree.  Nevertheless, an esperanto, in Esperanto, is "one who hopes".