auxiliary language

In SOCIOLINGUISTICS, the term is used for a language which has been adopted by different SPEECH communities for purposes of communication, trade, education, etc., being the native language of none of them. English and French are auxiliary languages for many communities in Africa, for example; Swahili is used thus in parts of East Africa. This sense must be clearly distinguished from the use of the term to mean an artificially constructed language, such as Esperanto.