Small update, problem solved, using the image of the 10.4 DVD installer and an USB stick, the Ibook is now back to French.

The USB stick was formated using my wife's Imac with the ability to boot a PPC based computer.

using the hard drive utility, the stick was properly set and the Ibook recognized both the internal and the stick as bootable  units (using OPTION key)

The install was smooth (only 40 minutes) so pretty quick  :beige: