Which constructed language (or 'conlang'), created in the late 19th century in the hope of promoting peace and international understanding, is the most successful in history, with speakers around the world and an original and translated literature?

Esperanto, created by the Polish doctor L. L. Zamenhof and introduced in 1887, is the most widely spoken constructed language in the world. Its grammar is extremely regular (16 rules without exceptions) and its vocabulary is based mainly on roots from Romance and Germanic languages. Although it has not achieved its goal of being a universal language, it has an active community of several hundred thousand speakers, annual international meetings and a rich culture of its own.