>Sumerian

Throwing a fun gee whiz:

Today they say the Sumerian language is an isolate language, unrelated to any after.

Funnily enough, the timing of its fall aligns around the time of the tower of Babel, if you go by the older Septuagint timeframe (different than what the 6th century jewish sect of Masoretes "helped" Christians to have by their Masoretic Text, the current basis of all OT translations).