Where do you think it's supposed to get the data from? By digging through your trashcan? No access - no data - no feature.

From the on-device memory, UI, camera etc.

Also: "Voice Translate allows you to break down language barriers during phone calls. Through Tensor G5, our on-device AI translates your call in real time in what sounds like each speaker’s voice"

They advertise on-device AI functionality quite a lot.