Esperanto
Who
L. L. Zamenhof, a Polish-Jewish ophthalmologist who created the language as a neutral means of international communication.
When
1887
Where
Białystok / Warsaw, then Russian Empire (now Poland)
Esperanto is the most widely spoken constructed international language, designed to be easy to learn and politically neutral. It was created in 1887 by L. L. Zamenhof, who published its first grammar under the pen name 'Doktoro Esperanto'. Zamenhof was a Jewish ophthalmologist from Białystok who hoped a shared language would ease tensions among peoples.
Sources
Part of “The Gifts of the Jews” — verified Jewish contributions to the world, with sources.