UNESCO offers an extensive General History of Africa. You can download each book free of charge:
Available languages are English, French, Arabic, Portuguese, Spanish, Italian, Fulfulde, Hausa and Swahili, but not all languages have each book translated in full. There are some languages which offer only the abriged version translated.
Here are some of the books offered on this site:
Methodology and African prehistory
Ancient civilizations of Africa:
Seventh-Eleventh century in English unabridged:
Twelfth-Sixteenth century in English unabridged:
All books are translated in their unabridged version in English, Arabic, French and Portuguese.