The sound_english.dat and sound_english.fat files are the core components of the English audio system. These files serve as a paired archive system within the game’s Dunia engine, containing everything from Vaas's iconic monologues to environmental sound effects like gunshots and jungle ambiance. Understanding the .DAT and .FAT Relationship

Can't change audio language, only english is available in Far Cry 3

Modders extract these files to replace voice lines or music.

: This is the data container. It stores the actual audio assets in a compressed format.