I have trouble thinking of kasha as anything but kasha. I thought that kasha is like a universally accepted concept, like how we just translate hryvnia into hryvnia.
"Hot cereal" should be accepted in place of porridge. I never once used porridge growing up except when telling "Goldilocks and the Three Bears" nor did i know what it means until i just recently looked it up.
I didn't even know that English had a word for anything resembling каша, попара (porridge with bread), помажда (porridge with semi-crushed wheat, in Bulgarian called трици), качамак (with maize flour) and other of this sort. The only time I showed what this is to a British friend of mine, he said it looks like "pig's food" so I thought British/American cuisine doesn't include каша-type dishes.
Porridge in English is not a countable object (i.e. a keyboard) so never uses "a"