Download Free Yoruba Audio Course
These free downloadable audio courses are for learning Yoruba. The same website has free courses for many other languages.
These particular courses are somewhat dated, having been created by the US Foreign Service Institute a while back.
However, Yoruba is a tonal language, and tones tend not to change too dramatically too quickly. Certainly nothing like slang! And, in fact, this series really gets deep into Yoruba tone drills.
Available in the Public Domain
Plus, it's available in the Public Domain which makes it possible to use and reuse for any reason.
Compared to more popular languages, it's difficult to find good materials for learning Yoruba, which makes these useful in many cases.