Do we speak out our intention to fast? Is there a special supplication to say before fajr or at Iftar time?
As a ruling we do not speak out our intentions in any act of worship.
The intention meant is your determination to fast tomorrow. If I know and determine fasting then I did fulfill the intention.
So every night I know and I am determined that I will fast tomorrow, and eating Suhoor is also an intention.
There is no specific duaa to be said in suhoor time, yet it is a blessed time where Allah descends to the first heaven and forgives those who ask for His forgiveness and answers those who ask Him subhanu wa taala.
Make sure not to miss duaa and Istighfar.
As for the only authentic duaa when breaking the fast is:
ذهب الظمأ و ابتلت العروق و ثبت الأجر إن شاء الله.
We say this duaa and we make duaa with a present heart.
As for the other famous duaa: اللهم لك صمت وعلى رزقك أفطرت ….
This is a weak hadeeth.