What ancient civilizations language is still indecipherable?

The language of the Indus Valley Civilization, often referred to as the Indus script, remains largely indecipherable. Despite numerous attempts by linguists and archaeologists, no definitive understanding of the script has been achieved, and its symbols have not been conclusively linked to any known language. The lack of bilingual inscriptions and limited context further complicate efforts to decode the script. As a result, much about the culture and communication of the Indus Valley people remains a mystery.