There is a quote by Johann Wolfgang which says: "Those who know nothing of foreign languages know nothing of their own."
I don't believe English should be the only language of learning and teaching in South Africa. In fact I'd argue we should learn not only a second but third language too.
To know another language can spark learning and an interest in so many other things: sports, politics, history,food, fashion and holidays. If English the only language in schools we limit ourselves to have more opportunities and to obtain new ideas.
One easy way to open a new door is to learn a new language. These days doors are open to those who are efficient communicators. It pays to be bilingual but it's even better to be multilingual