Hi,
At first thanks for helping me.
Actually Joomla made that folder for me so I copied and pasted en-GB.tpl_gk_yourshop.ini into the folder fr-FR and renamed it into fr-FR.tpl_gk_yourshop.ini. (By the way both file are translated in French).
Like it didn’t work I’ve decided to search the words “Shop cart”, “Items”, “Go to checkout” (because I wanna translate the VM cart module) on each files of my website folder but Notepad++ didn’t find anything! I even deleted en-GB.tpl_gk_yourshop.ini and fr-FR.tpl_gk_yourshop.ini but it didn’t change anything. Isn’t it weird?!