The language spoken in the Persian empires was Old Persian. It was the administrative language of the Achaemenid Empire and the Persian language used in official inscriptions and documents. Later, under the Sassanian Empire, Middle Persian became the dominant language.

Persian is the official language of Iran.

Words used in Persian language: Farsi or Parsi
Words used in English language: Farsi or Persian

Persian was the language of administration under the rule of Delhi sultanate.