I work at a tech startup in Cape Town (in the data analysis & visualization space.)
In my experience the challenge is that the local market isn't supportive or capable of supporting in some cases, and breaking into the international market with the weak rand is a tough nut to crack when your competitors all have several hundred mil in investment (x 17 for the exchange rate.)
So you sit with a product that fits locally, has some international potential but you can't really get enough sales locally to support an international launch and you kind of end up seeing the end of the runway whilst realizing that you're unlikely to have enough lift to get airborne by the time you reach it.
I'm sure that with enough funding this isn't as much of an embuggerance.
Any investors want to take advantage of the weak Rand? We have good devs and designers here, we speak English and we can get a lot done for about a 20th of what it would cost in the US...