Lead Developer
Hi there,
You can translate it here: https://translate.wordpress.org/projects/wp-themes/generatepress/fr/default
Unfortunately the French translation doesn’t have an editor for GP, as no one wanted to take the extra step that the French language admins require on WordPress.org to become an editor.
If you’d like to become an editor so you can approve the translation and future translations for GP in French, let me know your WordPress.org username and I’ll request it.