Many multinational and multilingual websites are configured to point the visitors to localized pages, on the homepage. This is done via redirects or changing the content that reflects the user's language. The recent Google Webmaster Central Blog introduces the new rel-alternate-hreflang annotation that can be used to specify such homepages. The annotation is supported by Google and Yandex.
The webmaster team has also shared an example to further explain the action. Supposedly, website example.com has content targeting users around the world as follows:
http://example.com/en-gb: For English-speaking users in the UK
http://example.com/en-us: For English-speaking users in the USA
http://example.com/en-au: For English-speaking users in Australia
http://example.com/: The homepage is a default page for the users worldwide and shows a country selector to users
In this case, the cluster of pages can be annotated by using rel-alternate-hreflang using the HTML link tags or Sitemap in the following manner:
<link rel="alternate" href="http://example.com/en-gb" hreflang="en-gb" />
<link rel="alternate" href="http://example.com/en-us" hreflang="en-us" />
<link rel="alternate" href="http://example.com/en-au" hreflang="en-au" />
<link rel="alternate" href="http://example.com/" hreflang="x-default" />
The new attribute value will signal Google and Yandex algorithms that the page doesn't target a specific language or locale & is the default page.
The same algorithm is applicable for homepages that dynamically alter their content on the basis of user's perceived geolocation or Accept-Language headers. The x-default hreflang value signals that such a page doesn't have a particular locale or language.The New "x-default hreflang" for International Landing Pages!,