Hreflang is a Minor Canonicalization Signal
Google uses hreflang as a small signal when picking the canonical version of a page, but this needs to be backed up by consistent signals provided by rel canonicals, internal linking and sitemap files.
Google May Fold Together Similar or Duplicate Hreflang Versions
Google may fold together hreflang versions of a page if the content is similar or the same, as it doesn’t make sense for both versions to be indexed.
Implement Clear Canonical Version Per Country & Hreflang Between Equivalent Canonical Versions
Don’t specify a canonical between different country versions of a page, because Google will likely only index the preferred version. John recommends having a clear canonical version per country and implementing hreflang between the canonical versions for each country.
After Indexing Google Checks to See if a More Relevant Page Can Be Swapped in
After pages are added into Google’s index, it then checks if there are any different URLs that should be swapped in because they are a better fit for the user.
Hreflang Alternates Can Still be Shown in Search While Technically Non-indexable Duplicates
Pages identified as duplicates which are not technically indexed may still be shown in search if they are an alternate hreflang version which is similar to the canonical version.
Each Language Version has to be Crawled & Indexed at Least Twice for Hreflang to Work
Different page versions need to be understood before hreflang annotations can be used, so individual language versions have to be crawled and re-indexed at least twice to see the annotations and confirm them. John recommends using hreflang for stable content but keeping quickly changing content i.e. news in one location.
Google Uses X-default if it Can’t Find a Relevant Country + Language or Language Result First
Google will first try to find a relevant result for the user’s particular country and language combination e.g English in Canada, then will look for a generic language e.g. English, then will use your x-default specified result if it can’t find either.
There are 3 Levels of Hreflang: Language, Language + Country & X-default
The 3 levels of hreflang targeting are language, language + country and x-default which is used to specify default targeting for pages that haven’t been explicitly targeted to a particular language.
Hreflang Doesn’t Cause Content Duplication as URLs Are Switched in SERPs
You don’t need to worry about content duplication with hreflang because Google will recognise URL clusters and the connections between them and swap the URLs in the search results to show the most relevant page for the user.