Out of a total population of 61 million, you have a middle class measured at around 15 million with over 8 million individuals making up the country's gaming market by 2027. This is in contrast with the smallest country with a Runescape server, Lithuania, with under 3 million people total. Never mind that Lithuania is also close to other European servers whereas for many South African players, high-demand content like PvM is simply out of the question.
Furthermore, in recent years, the gaming market has exploded not just in South Africa but in Africa in general. Adding servers could serve neighboring countries using either English, French, or Portuguese, languages that Runescape currently supports.
Jagex would do well to support the South African community and tap into potential for Runescape to reach a large, dynamic, and tech savvy audience by introducing South African servers.