It’s unlikely you’ll ever create web page variations targeting all languages and locations. Sometimes, you’ll need to have to give Google an indication of what do to whenever a offered place or language isn’t obtainable or doesn’t exist. An x-default tag would be the URL that Google displays.  Yandex: Russia’s https://bookmarkyourpage.com/story4154376/what-does-canonical-link-tag-not-found-mean