Interlingue was created by the German-Estonian, Edgar de Wahl, in the early 20th century. It was once considered a serious rival to Esperanto because of its extreme naturalism, its great intelligibility to the whole Western tradition, its use of Latinate heritage combined with international vocabulary, its good intelligibility to Germanic as well as to Romance, and its great mixture of simplicity and analyticness. Most speakers eventually left and joined Interlingua, but many more remain today, especially in central Europe.

There is even an Interlingue Wikipedia!

Lesson One

Lesson Two

Lesson Three