I can send you the files I made (fr.hlp and fr.tr for first boot screen of the LiveDVD) and (fr.hlp and fr.tr for grub-gfxboot Mint screen). I made them last days for Mint 6 Felicia.
If you received my personnal message, I said that I had modify directly isolinux.cfg and isolinux.txt in isolinux directory of the iso file to have french translations. Now, I can choose english or french in liveDVD boot screen without problems.
For grub-gfxboot, only menu list is still in english, else, it's translated in french. I made a gnome.message with english and french files, but I put a file named : lang, where I defined only : fr . When I boot, a part of the screen is in French (Bottom of the screen).
Tell me if you are interested by my files, I will give you them.