SDL is written in C, but bindings are available for multiple languages, including C++ and C#. As it happens I was actually using it with C++. And there are other libraries you could use instead, like GLFW or Allegro.
I’ve never thought of C as being that much lower-level than C++, but I guess everything’s relative.






Is the main issue really tracking and consolidating microdonations, or is it transferring credit between these donation systems and traditional finance entities like banks and credit card networks?
From what I’ve seen, efforts to develop microtransaction/microdonation systems generally seem to have trouble with regulatory compliance, either through legitimate legal requirements that force them to do things that seem nonsensical to their users (My guess is that the registered servers issue OP mentioned with Flattr came down to this), or due to greedy intermediaries stalling and witholding under false pretences while they hold out for a bigger share of the money, without appreciating the already extremely thin margins involved.