The hreflang “x-default” attribute value indicators to Google algorithms the site doesn’t target any certain language or locale which is the default page when no other webpage is best suited. Picture you might have an e-commerce Web page that’s available to people in copyright in the two English and French. https://addons.prestashop.com/en/seo-natural-search-engine-optimization/30904-automatic-hreflang-tags-canonical-tags-all-pages-seo.html