"Does anyone know if the grit paper's rating/index is the same all over the world ?"

Frenchy, do you really expect a county that cannot figure out metric to be on the same system as anyone else? <img src="/images/graemlins/blush.gif" alt="" />

There are at least three different systems for sandpaper grit values:

Coated Abrasives Manufacturer?s Institute (CAMI) (used in US)
Federation of European Producers Association (FEPA)
Japanese Industrial Standard (JIS)

I do not know much about the Japanese standards, but the CAMI and FEPA are close enough for typical wood working, i.e. sandpaper in the 60 - 250 grit range. At the higher end grits (very fine paper) FEPA values will be higher than CAMI values for the same type of paper.

FEPA grit values should have a "P" in front of the number. A CAMI 600 grit paper would be about P1200 on the FEPA scale. A CAMI (United States grade) sandpaper of 1000 grit would be about a P2500 (FEPA scale).

I do not know what you will find in France, but if you see "P grade" it should be on the FEPA scale.

I do not know for sure, but I suspect that a 1000 grit to me in the US would be about a P2500 for you.