Porchetta is a kind of roast pork, but it's not a flæskesteg, although flæskesteg is the most common style in Denmark. It's my understanding. “Flæskesteg er en traditionel dansk ret.” according to Wikipedia.
Flaeskesteg is not an English translation. It doesn't have to be a perfect translation just like hygge doesn't have a perfect translation into English that conveys the entire meaning of the word. But for flaeskesteg, roast pork is close enough.