What does mfethu mean?

Mfethu means “friend”

Used as a term of address for those male persons engaged in the same movement.

In other words, my brother, my pride, my crew, home boys down in Southern Africa

Tsotsitaal and Camtho

"Tsotsitaal is a vernacular derived from a variety of mixed languages mainly spoken in the townships of Gauteng province, but also in other agglomerations all over South Africa."

^{https://en.wikipedia.org/wiki/Tsotsitaal_and_Camtho}