Which language was used by Darius I and Xerxes I for official inscriptions?

Official royal inscriptions from the reigns of Darius I and Xerxes I were typically trilingual, featuring Old Persian, Elamite, and Akkadian.12

While Old Persian served as an official language for these rulers, it was not the only language used in the Achaemenid Empire. The empire’s administrative bureaucracy relied heavily on Aramaic, and Elamite was commonly used for administrative records in regions such as Persis. The Old Persian texts were written using a simplified, quasi-alphabetic system of cuneiform, which was adapted specifically for the language during the time of Darius I.132