The weapon is located at Libertalia, found inside the captain's cabin at the top of the compound, lying on top of a wooden crate. The crate is located immediately across the room from the door, beside a burning lantern.
Behind the scenes[]
While not a perfect French translation (actually translating directly as "The Terrible Gun," with "terribles" unnecessarily pluralized), the weapon's name, along with being a unique variant of a combat shotgun inflicting higher damage but with higher recoil and even sharing the fact of being found in a raider stronghold, means it is most likely a reference to The Terrible Shotgun from Fallout 3.
The name of the weapon is a reference to the 1929 French novel and its 1959 film adaptation Les Enfants Terribles.
Gallery[]
Le Fusil Terribles in the Libertalia captain's cabin