Create it manually. Right-click in the right pane of the Registry window > New > String Value > Name it Language > Set value to en-US (or your choice).
Once the packs are installed, you can refine your settings in the main menu: far cry 4 language pack install
In the tab (or Language tab in older Steam versions), choose your desired language from the drop-down menu. Create it manually
Some users report that Steam might not provide all voice-over files even after switching languages, which may require a verify integrity of game files check. 3. Epic Games Launcher String Value >
sound_english.dat and sound_english.fat (Place in \data_win32\ ).