One SEO professional was concerned about using hreflang across domains. In a hangout, they asked John Mueller about this.
Their situation is they are localizing their website with a subdirectory structure. They have a TLD, covering the main audience.
Due to some reasons, they had to get another domain for a new locale. How should they approach a localization there?
Should they introduce an alternate tag for the other domain? As their global domain is currently ranking in that locale, they are going to want the newer domain to appear there.
John answered that the example structured data, or the hreflang annotations that the SEO professional provided, looked okay.
However, one of the things John noticed is that they have an x-default setup on both of these sites separately.
And from their perspective, they really need to just have one x-default. One way to look at this is, regardless of if it’s on one domain or on multiple domains, on a per page basis, all of the hreflang annotations should match up.
And it should be clear that for any particular page on this site, if they have a requirement for what they would like to show users, the hreflang annotations guide them to a specific location. for example, if someone has languages, for example Turkish in Turkey, if someone comes into your website like that, and they rank one of these pages in the search results, it should be clear that from the cluster of hreflang annotations that you have exactly which page would be the optimal one to show.
This is the general guidance that John recommends.
It doesn’t matter if this is all on one domain, or across multiple domains. It should just be one clear place, per country and language.
The other way around is a bit more flexible in that you can have multiple countries and languages on one page.
Mapping from country and language to a page should be done in a one to one ratio, but the mapping of per page, which countries are on that page, or which language is on that page, are entirely up to you.
This happens at approximately the 26:57 mark in the video.