Magento-2-HrefLang
In case there are several CMS pages with same identifier, under different stores, page will display, for example :
<link rel="alternate" hreflang="en-gb" href="https://magento-store-1.com/cms-page" /> <link rel="alternate" hreflang="en-us" href="https://magento-store-2.com/cms-page" />
Current page will be included - https://en.wikipedia.org/wiki/Hreflang
In case there is page for only one store it will be ommited.