Is c language allowed in this jam?

Yea of course, I do not see why that shouldn't be allowed.

You can use anything as long as it runnable.

 Tip: if you manage to run your game in browser (in case of C, you can use emscripten) you will most likely get more ratings and reviews. My most recent jam entry used C++ via emscripten, and emscripten has  SDL built in so you are set to go