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.