As noted in Plugin Translations for All Plugins from 2015, plugins on WP.org are able to benefit from translations available and maintained via GlotPress. As such, we should confirm that the translations listed in https://github.com/mailchimp/wordpress/tree/main/po properly exist on the plugin's GlotPress instance and if so then ensure that all strings are marked as translatable in the code and then remove the po directory and its contents as no longer necessary.