SEO Localization Google Hreflang Pro

What does the Google Hreflang Pro module do?

Provides SEO signal(s) to Google and other search engines which language(s) | country(s)/region(s) content is available for. For multi-lingual shops, it provides SEO signal for auto or visitor select support for language.

The hreflang tag (introduced in 2011 by Google/Yandex/Bandu) (also referred to as rel="alternate" hreflang="x") tells search engines which language you are using on a specific page and what other languages and optionally country/region the page is available for. In 2013 hreflang x-default was introduced as signal for a auto-detect of language and/or visitor language select.