The Dunia engine used by Far Cry 3 utilizes a paired file system for its data:
Short for "File Allocation Table," these small files act as an index, telling the game engine exactly where to find specific sounds within the massive .dat archive. Why You Might Need to Download or Restore These Files The Dunia engine used by Far Cry 3
Can't change audio language, only english is available in Far Cry 3 The Dunia engine used by Far Cry 3