Lingua francas are those languages that are used for communication by people in different communities who do not speak the same languages. Such languages are usually not their first languages and in rare instances not formal languages too.
Usually these are put in place to solve the communication barriers as common ground since everyone involved seems to have a first language that it different from the others. It should be noted that such languages are very important in Africa because African countries have plenty of indigenous languages for example, Nigeria is estimated to have more than 500 indigenous languages while Uganda has about 53.
Swahili happens to be the lingua franca in a number of countries in Africa where it serves as on in a country but also as a lingua franca for a number of countries. For example, as much as Swahili is a lingua franca in the whole of Kenya, Tanzania, Rwanda, the Democratic Republic of Congo, Burundi, the east of Uganda and some parts of Zambia too. This languages still can be called the lingua franca of all those countries put together.
Afrikaans came up as a common language to ease communication especially with the white rule in South Africa although its importance has waned over the years with important institutions that were named in Afrikaans having their names changed to English. However Afrikaans holds a special place in Namibia to date with the language being common in Windhoek, the capital city of Namibia.
Arabic and its various varieties is the lingua franca of so many African countries majorly found in the North and in the horn of the continent and the countries here include Ethiopia, Algeria, Mauritania, Morocco, Djibouti, both Sudan and South Sudan, Libya, Chad, Tanzania etc.
When it comes to West Africa, there are several languages too that act as lingua francas to certain communities of people and these are;
Wolof
Manding
Hausa
Krio etc.
It should be noted that there are the famous lingua francas in Africa that came about as a result of European scramble and partition of the countries and these are Portuguese, English, a little German, Spanish and French. A further uniting factor here is professional translation services that bring about more effective communication when it comes to languages one cannot understand and with no lingua franca to act as a middle ground.