> Is there any French install doc for NetBSD?

 Non. 

 Traditionally french is the least language the installation file
is translated to, if ever. The only other language the installation
procedure was translated to - to my knowledge - german. But this was
the 1.2 release...

> I don't know anything about NetBSD, and i lose my trying to install it on 
> my Amiga 1200...

 It's easy. Print out the installation file. Read it. Read it again.
Understand it. Then go ahead and install. You will learn very much about
your Amiga and NetBSD while doing so.

-- 
Markus Illenseer