This attribute comes in clutch for pages that serve as the default version for end users whose language or locale doesn’t match any hreflang tags.  It may also assist you to incorporate the default "x-default" tag for users from international locations for which the language is not really configured on https://addons.prestashop.com/nl/seo-zoekmachineoptimalisatie-vermelding/31857-automatische-google-rich-snippets-json-ld-opengraph-seo.html