balam jAn,
the language is called Persian in English, not Farsi, which is the same thing, the Latin translation of Parsi or Farsi = Persian
Farsi is the arabicized form of Parsi, due to a lack of the /p/ phoneme in Standard Arabic. now you can chose to call it Parsi, or Farsi when you are talking to Iranians, but when you speak in English, Persian is still used since they didnt get invaded.