[FabHK]

Which makes sense, as there can't be "negative" objects, mostly.

Building floors are more ambiguous - there can be basement, ie "negative" floors. So, floors in continental Europe are generally indexed 0-based (basements ..., -2, -1, ground floor = 0, upper floors 1, 2, ...). A German friend of mine caused some confusion when she checked into her student dorm at a US college, and having being told that her room was on the first floor, asked whether there was an elevator, as she had heavy suitcases.

[skydhash]

In French, the first floor is called "Rez-de-chaussée" and the uppers are what called "Etage". So it's actually 1 based.

[FabHK]

But the etage above the Rez-de-chaussée is 1, correct? The Rez-de-chaussée then is 0. That is 0-based indexing.

  US  D  F
   3  2  2
   2  1  1
 __1__0__RdC
  B1 -1  je ne sais pas

[skydhash]

There is no Etage 0. People will just confusingly look at you if you ever said that. And the "Je ne sais pas' is called "Sous-sol"

[gwhl]

In a lot of elevators rez-de-chaussée is labelled 0. We just don't use that when communicating

[scraptor]

You can have multiple basement levels, which get numbered again. 1er Sousl-sol, 2eme Sous-sol etc. The ground floor might not be explicitly labeled as zero but the number between "one up" and "one down" is still zero.