Drag and Drop : Translate in french "Are you sure you want to upload" message on Firefox when browser's locale is french

This tasks consists just in adding a hack at the place where the message "Are you sure you want to upload" is generated : use a "if" statement to change the behaviour depending on the locale of the browser (feel free to use all your language knowledge there to add other languages )We don't want for now to use the full internationalization framework