There are a few SEO’s who have suggested that you only need a HREFLang entry on the Home Page of the site. This is incorrect.
This is not very common, but a few sites have only used HREFLang tags on their home pages. Unfortunately, Google’s sample code only shows the home page version of a URL resulting in some interpreting that to mean you only need them on home pages. In one case the SEO implementing it only on the home page told me that “Google is smart enough to figure it out – we just need to give them the template and they will understand.” Unfortunately for the client Google did not understand it and was showing the incorrect page in local markets.
Clarification: The hreflang element must be added to any and all pages that have an alternate version or included in an xml sitemap and not just home pages.