Nothing is certain in Africa. One of these things is 'having a shower tonight'.
Mostly, you're in one of the following situations:
- You're in a Village/with local people.
Someone will show you a place with 'some' privacy. This place often doubles as toilet. A bucket with water will be provided.
- You're in a hotel or campsite.
These places have a designated place for washing.
- You're bushcamping
just whash before you go to bed. A kind of plastic/rubber sheet to stand on is handy. Otherwise you'll be showering in mud pool soon.
And if none of the above happens, it's dark early, and there's little lighting, so you can have a quick shower behind the car, or you'll do with brushing your teeth and a washing your feet, hands and face.
I never used a curtain, and often took advantage of darkness. If you feel uncomfortable being naked in the dark, I suggest you take a shower curtain.