This attribute comes in clutch for pages that serve as the default Model for buyers whose language or place doesn’t match any hreflang tags.  It will also permit you to include the default "x-default" tag for consumers from countries for which the language is just not configured on your web https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-google-rich-snippets-json-ld-opengraph-twitter-tags-schemaorg.html