Elamite

Elamite is a language isolate of ancient Elam in southwestern Iran (modern Khuzestan and Fars), spoken from at least the 3rd millennium BCE until c. 6th century BCE — and used as one of three administrative languages of the Achaemenid Empire (with Old Persian and Akkadian) until the 4th century BCE. Three distinct script traditions: Proto-Elamite (~3100 BCE, still undeciphered, the oldest writing of Iran), Linear Elamite (~2200 BCE, partially deciphered in the 2020s by Desset, Vidale et al.), and the Akkadian-style Elamite cuneiform used most extensively, including in the Persepolis Fortification archive of ~30,000 administrative tablets and the trilingual Behistun Inscription of Darius I.