Since a while, Google has begun testing a new feature, which is now known as a Webmaster Tools href lang debug tool. This tool will be available under the International Targeting section of “Search Traffic.”

It will help to debug two main things; Missing return links and Incorrect hreflang values.

Google Webmaster Tools

What is international targeting?

If you own one or more websites designed for users in a specific country speaking a specific language, you want to make sure that search results display the relevant language and country version of your pages. To ensure that your content reach the correct audience, you will use two general mechanisms; URL-level targeting and Site-wide targeting.

Once you have configured multi-language or multi-regional sites and pages, you can use two sections in the International targeting pages to keep your worldwide presence healthy:

The Language section—this helps you ensure your hreflang tags use the correct locale codes (language and optional country).  More commonly, you can make sure that alternate pages have tags that link back to the pages for your site.

The Country section—you can use this tool to set a site-wide country target for your entire site, if necessary.