Gabriele Sommer, 'A Survey on Language Death in Africa', in Brenzinger (2012) Language Death, p. 351. See Hammarström, Harald; Forkel, Robert; Haspelmath, Martin, ed. (2023). "Hamba". Glottolog 4.8. Jena, Jerman: Max Planck Institute for the Science of Human History.Pemeliharaan CS1: Tampilkan editors (link) )
Hammarström, Harald; Forkel, Robert; Haspelmath, Martin, ed. (2023). "Okwa". Glottolog 4.8. Jena, Jerman: Max Planck Institute for the Science of Human History.Pemeliharaan CS1: Tampilkan editors (link)