The hreflang HTML attribute tells Google the language of your content so that it can serve your content to the users who are searching in the language that your page is in. For example, a Spanish hreflang tag will tell Google to serve that Spanish version of the page, rather than the English version of the page, to users whose search engine language is set to Spanish. The hreflang tag denotes that the page is an alternative to another page that’s the same content — just in a different language. Hreflang is often used to account for currency, shipping, or cultural differences.
Google uses ISO 639-1 tags to represent languages in code.
An hreflang tag can be implemented in the on-page markup, the HTTP header, or the sitemap as follows (Spanish is shown in the following example using the “es-es” annotation):
<link rel=”alternate” href=”http://example.com” hreflang=”es-es” />