The Call of Duty: Black Ops 3 (BO3) English Language Pack is a set of localization files required to change the game's display text, menus, and audio to English. Depending on your platform and region, this is handled either through official store settings or manual file replacement. Official Methods by Platform PC (Steam):
One of the reasons Black Ops 3 has survived so long on PC is the Steam Workshop. Custom Zombies maps are massive. But for a long time, many custom maps were built by creators who only included English voice lines and text.
A significant issue for Black Ops 3 players is region locking. Unlike many modern titles that allow free language switching via console settings, the language for Black Ops 3 is often tied to the region of purchase. For instance: