During the most recent Q&A webmaster session, which occurred on November 12, 2021, Google’s John Mueller was asked a question pertaining to multilingual--and possibly, multinational--sites.
The video below has been queued to the 14-minute, 13-second mark, when the question was asked:
Basically, the person who asked the question stated some details about his site:
-He had the Yoast SEO plugin, which can create canonicals
-He had another plugin (WPML, possibly) which, as a multilingual plugin, creates hreflang
Each of these (canonicals and hreflang) is a way of specifying alternate URLs. So, I can see why he’d have the question that he did: would these, in any way, conflict?
John’s response was:
“I mean, I don't know exactly what these two plug-ins do. So it's kind of just-- from an overall point of view, if you have a page that has a rel=canonical on it, you're essentially with a canonical saying, ‘The link that is mentioned there is the preferred URL that I want’.
“And if it's the same page, then that's perfect because then it kind of gives us confirmation that this page is the one that you want to have indexed. And the rel=alternates basically mean there are alternate versions of this page as well.
“So with different languages--for example, if you have one page in...English, one page in French, you would have the rel=alternate link between those two language versions.
“And it's not saying that the page where that link is on is the alternate. But rather, it's like these are two different versions, and one of them is in English, one of them is in French.
“And they can both be canonical. So having that combination is usually fine.”
But...Don’t Canonicalize Across Different Languages
“The one place to watch out a little bit is that the canonical should not be across languages. So it shouldn't be that on your French page, you have a canonical set to the English version because they're different pages, essentially.”
“But the French page can be canonical [to a French page], and the English page can be canonical [to an English page].
“And you have the alternate link between the two. And that's essentially a good setup.”
For confirmation, John was asked, “Okay, so it can be canonical and alternate on the same page,” to which he replied, “Yes.”