Do you speak Esperanto?
On a pedestrianized street in Prague, we encountered this highly-noticeable advertisement for the benefits of learning to speak Esperanto.
For those who may not remember, Esperanto is an invented international language touted as a way to world peace through everyone sharing a common language, which, its enthusiasts hoped, would eventually replace all others.
Its more modest claim today is that it is 'the most widely spoken constructed international auxiliary language.' It was first invented in 1887 by a Polish ophthalmologist, L. L. Zamenhof. On a more practical level, Zamenhof thought that if it became a universal second language, books would only need to be translated into Esperanto for everyone to understand.