How do i make my language a GCSE in the UK?

i speak Shona which is from Zimbabwe, I recently wrote my GCSE and many of my friends had to opportunity to write their mother languages e.g. Turkish. It was a great advantage because they managed to get A*'s, i would have loved to write a shona GCSE. I was wondering how do my make my language a GCSE for schools, i would thinks it gives you more GCSE s and it's a great chance for other children.