It's the same in most of the commonwealth (it's the case in South Asia and Kenya as far as I know). Going by the other comments, it seems like premier étage = first floor. So, what do you call the ground floor in French?
"The ground floor" in France is "le rez de chaussée". You'll see "RC" on the elevator button. "Rez" is an antiquated word meaning "level". "Chaussée" is a slightly less antiquated word meaning "street, carriageway, causeway".
And, just to add more confusion to the conversation, there are many places in the English speaking world that have both a "ground floor" and a "first floor" one level higher.
More likely, you will see "0" on the elevator button in France to indicate the ground floor.
Its my understanding that a Frenchman hearing premiere étage will not think of the same level asme hearing 1st floor.
If I say "no", are you thinking "maybe"? One can only say what is and if the other person is using a different paradigm, he will figure it out eventually...or perhaps you can explain it. But if you start to assume how the other person thinks and translate accordingly, it will be a bumpy ride. If you are compelled to tell someone about what floor something is on, maybe you should check with them about what floor this one is where we're standing. With that confirmation of your friend's "floor-counting paradigm", you may proceed safely. If that is too burdensome, imagine how it is when we assume what others must be thinking and never give them the benefit of clear communication.