No single entry on Africa, but has entries for langugage families and language situation in specific countries. International Encyclopedia of Linguistics. Edited by William Bright. Oxford University Press, 1992. 4 v. Entries are provided alphabetically by language or topic.
Excellent bibliographies accompany each article.
Campbell, George L. Compendium of the World's Languages. 2 v. Concise facts on phonology, morphology, and syntax, for each language. The Languages of the World. A text sample and a little information are given for each language. The Major Languages of South Asia, The Middle East, and Africa.