I believe #1770 makes more sense and does not necessarily mean we should provide a default .po/.mo file, as @benword said it is not really the point of a starter theme, however is the theme correctly uses gettext calls it should also load the textdomain.
This is quite simple to do, still it belongs on a starter theme as being almost required on all projects.
I suggest adding it to
'dir.language' => get_stylesheet_directory() . '/lang/',
And after that:
/** * Make theme available for translation */ load_theme_textdomain('sage', $paths['dir.language']);
And creating a lang folder, not really needed to add a .po file in my opinion.