Hey J.S. the term motivational speaker is broad. You could be a business speaker, a keynote speaker or a motivational/inspirational speaker.
Back to your question. Don't become a speaker until you've become an expert at something. Find out what you are an expert at and then speak on that.
Your expertise is your "qualification needed to become a reputable motivational speaker".
There are no formal qualifications in the sense of a university degree or diploma (not in South Africa in any case).
There are a number of speakers associations around the world. Try the Global Speakers Federation or National Speakers Association. Some of these organisations have "graduate" programmes to get you up to speed.
Of course, if you want to hone your skills and do your 10 000 hours on your craft (Outliers, Malcom Gladwell), then you should seriously consider joining Toastmasters. Here you can, in an environment of acceptance and trust, practice and mess up your speeches and nobody will judge you.
I hope this has helped.