As for flying with TK to JNB–you would be flying with A330/340–the C seats are a lie flat angled version of Sogerma. If you are lucky–you might find a good angle for your sleep–otherwise the seat is good for lounging.
Regarding food service–the quality and quantity are great–presentation is good and F/A strive to give their best–the service with the trolley during dessert and digestiv service remembers of the old F class service–very nice. I would says It is one of the best C class service at the moment
Regardng safety procedures–here is the nemesis of TK–often the crew lacks professionalism and consistency. In this point they have to improve themselves as they are not in the same level as LH or SQ.
About communication on board–the F/A are in general not frequent in speaking English( well for my flights they definitely struggle )–but just talk to them directly and they will give their best. Often they tend to communicate with Turkish pax more than with the foreigners-but do not get initmidated–just tell what you need and they tend to it.
Wish you a great flight !!