Sadly the Apple guarantee only covers manufacturing faults. It was a physical accident and would not be covered. The same goes in respect of Apple care, which is an essential cover to have but it is restricted to manufacturing faults.
I'm sure you will appreciate it was not Apple's fault.
There are two other possibilities (though I don't know if it applies in France as it does here}.
If you made the original purchase using a credit card, here in England many credit cards give insurance cover for purchases over £100 in value.
Another option, your own household insurance may cover it.
Wish you well.
Oh, and your English is OK.
Apple's warranty will not cover accidents.
You can get a replacement glass for your iMac and install it yourself.
I think it is around $150.00 to $200.00.
The glass is only held by magnets.
The hardest part is to keep dust and particles from getting stuck between the glass and the screen.
Test the iMac before you buy a new glass, to see if it got dammaged by the fall.
Make sure there is no glass pieces in the computer, vacuum around the screen, before you install a new glass.
You can find a guide on replacing the glass panel on ifixit.com and you can buy the glass on the internet.
Sinon, tu peux le faire réparer dans un centre de service Apple, mais $$$!