来源： “The World Atlas of Language Structures” . , Bernard Comrie and David Gil and Martin Haspelmath and Matthew S. Dryer · Oxford University Press

来源： “Ethnologue: Languages of the World, 16th Edition (2009)” . , M. Paul Lewis · SIL International

来源： “Endangered Languages in Central Africa” (163-178) . Bruce Connell (2007) , Matthias Brenzinger · Mouton de Gruyter

来源： “Atlas of the World’s Languages in Danger” . Christopher Moseley (ed.) (2010) UNESCO Publishing

来源： “World Oral Literature Project” .

来源： “Loss of Linguistic Diversity in Africa” (157-170) . Maarten Mous (2003) , Mark Janse and Sjimen Tol · Amsterdam: John Benjamins