DMC, before dropping 10 or 15 grand on a PPL I'd suggest making a few phone calls. Start with Airservices - I have no idea if there is any leeway for the educational requirements but you may be able to gain recognition for something that would suffice. Probably helps if ya speaks proppa
Next stop would probably be SACE - surely someone there would be able to advise your options for doing year 12 English in SA:
www.sace.sa.edu.au Even the local high school might be worth a try.
Doing a PPL for the sake of gaining knowledge that will be relevant to ATC is a pretty expensive thing to do - the vast majority of relevant knowledge could be acquired by reading, asking questions & going for a few flights with the local aero club. By all means do it if you feel the need but not just for the sake of aviation knowledge.