In ME1, everyone calls the Citadel, Citadel. Sovereign calls it Citadel. The damaged VI on Ilos says Citadel. Vigil says Citadel
In ME2, everyone calls the space station Citadel
At the beginning of ME3, Anderson says Citadel. When talking with the council, the word catalyst is mentioned. Its a part that is missing that would complete the device. After the coup the word catalyst in mentioned again. Everyone is still calling the Citadel, Citadel. Even Javik refers the Citadel as Citadel. On Thessia, Vendetta mentions catalyst as well as Shepard.
On Chronos Vendetta says in your cycle its known as the Citadel. Interesting. So if Vendetta calls the Citadel catalyst, why didn't Javik and the two VI's on Ilos call it catalyst?
Turns out Vendetta was incorrect. The catalyst is the leader of the reapers. But Leviathan calls it the intelligence. Why did the catalyst say its the catalyst when Leviathan calls it the intelligence? Did the Insuannon, the species before the Protheans, call the citadel something different?
If previous cycles were able to translate the plans to build the device, wouldn't they of been able to know the Citadel is needed for the device to work? Or was it the Protheans who decided to call the Citadel something different as a safety precaution? Or maybe not all Protheans called it catalyst, but Citadel and it was the group that was building the crucible that called the Citadel, catalyst. Vendetta did say it was programmed not to say what the catalyst is until the Crucible is completed.