Which language became the official language of the Achaemenid Empire?

While the Achaemenid Empire was linguistically diverse, it did not have a single official language in the modern sense. Although Old Persian was the language of the Persians, it was not the primary working language of the imperial administration.12

Instead, Aramaic served as the language of much of the empire and was likely the most widely used language within the imperial bureaucracy. Additionally, Elamite was extensively used for administrative purposes, as evidenced by the discovery of numerous administrative documents on clay tablets at Persepolis. Royal inscriptions were typically produced in a trilingual format—incorporating Old Persian, Elamite, and Akkadian—to ensure they could be understood across the diverse regions of the empire.12