Lead Developer
Sorry, I’m pretty confused here.
Are you wanting to use files to translate, or WordPress.org?
If you translate the theme here and get the translations approved, your site will be translated automatically: https://translate.wordpress.org/projects/wp-themes/generatepress/fr/default
If you want to use files, you need to use a program like Poedit, and upload the files to your server as explained here: http://wordpress.stackexchange.com/questions/185999/override-parent-theme-translation-on-child-theme
Those are the only two options for translation at the moment.
The first option is much easier, and benefits everyone.
The second option is a bit harder, but necessary if you’ve changed any text strings in the theme and need custom translations that others won’t need.