This attribute is available in clutch for pages that serve as the default version for customers whose language or location doesn’t match any hreflang tags.  It will also enable you to include the default "x-default" tag for users from international locations for which the language is not really configured on https://www.presta-addons-modules.com/en/opencart-seo-automatic-google-rich-snippets-json-ld-integration-opengraph-twitter-tags-schemaorg.html