Hreflang tag

Hreflang tags are a technical solution for sites that have similar content in multiple languages. The owner of a multilingual site wants search engines to send people to the content in their own language.

What are hreflang tag attributes? 

The hreflang attribute adds a signal to search engines that a user querying in language "x" will want this result instead of a page with similar content in language "y". ... That means that other SEO factors may override the hreflang attribute and cause a different version of your page to rank higher.

The hreflang attribute tells Google which language you are using on a specific page, so the search engine can serve that result to users searching in that language.