Getting your Assassin’s Creed III (AC3) audio to work in English usually depends on whether you're missing the actual files or just need to toggle a setting.
Sometimes the English files are installed, but you still can't hear character voices: download link assassins creed 3 english audio voice file
which provide a "One Click" mod manager to swap language files in region-locked versions. Audio Extraction Getting your Assassin’s Creed III (AC3) audio to
Replace Configuration: Copy the downloaded localization.lang file into the main game folder, choosing "Copy and Replace" when prompted. Install Audio Pack: Navigate to the Sounddata/PC folder. Install Audio Pack : Navigate to the Sounddata/PC folder
Official Ubisoft Method: On Ubisoft Connect , you can often download additional languages by selecting the game in your library, going to Properties, and choosing English from the Language section. How to Install English Audio Files