One place you can look into if you want to know more about this is Louisiana Creole. Creole is a "pidgin" language, a mix of multiple languages into a new language which borrows words from all of them. Louisiana Creole is a mixture of French, African languages, and Native American languages; It is still spoken to this day.

It's not exactly an answer to your question, but I think that it is likely that because the African slaves were interacting with other slaves who might not speak the same languages, a pidgin language developed between them.