Is this a sysprepped image?
You need to go back to a working setup on your master machine, install the French language pack, test, and then prepare your image for distribution as you did for your current image.
By the way - is the French language pack intended for the operating system or for MS Office in your image?
What language is your native Win 7 installation?
Basically, there is not much detail in your original posting to help determine a course of action.