Interlingue is a constructed language. It was called Occidental between 1922 and 1947. It was created by Edgar von Wahl, one of the first Esperantists. Von Wahl was from the Russian Empire. He spoke German. He had natural ability in languages. He is often called de Wahl.
De Wahl was not happy with Esperanto. He decided to create a language called "Occidental". He published it in 1922. In 1947 the name of the language was changed to Interlingue.
- Haas, Fritz. 1956. Grammatica de Interlingue in Interlingue. Interlingue-Servicie Winterthur (Svissia).  (in Interlingua)
- Jacob, Henry. 1947 Occidental (1922) by Edgar de Wahl en 0' A Planned Auxiliary Language Publicate: London, Dobson, London. 1947  (in English)
- Rodriguez, José María. 1999. Breve gramática de Interlinguie/Occidental en Gazeto Andaluzia (órgano oficial de la Asociación Andaluza de Esperanto) N° 57 marzo 1999.  (in Esperanto)
- Stenström, Ingvar. 1997. Occidental-Interlingue: Factos e fato de un lingua international. Societate Svedese pro Interlingua. ISBN 91-971940-2-6. (in Interlingua)