There’s the Google help page I already linked to, which explains the correct use of the attribute. You use it to mark an alternative page in another language. If there is no alternative page, then obviously you can’t use the attribute.
Maybe you’re thinking of the lang attribute? eg.
<html lang="en-GB">
https://html.spec.whatwg.org/multipage/dom.html#the-lang-and-xml:lang-attributes
@chrisofarabia, @TechnoBear and @Mittineague have already answered all questions.
I just want to point to what I see as the cause of the error message. 
According to your screenshot, you have given the alternate page the same url as the canonical page:
2 Likes
This topic was automatically closed 91 days after the last reply. New replies are no longer allowed.