Google announced on Monday that it is adding a new feature to Google Webmaster Tools to make it easier to debug rel-alternate-hreflang annotations. These are the attributes Google uses to serve the correct language or regional URL in search results.
Google's Maile Ohye talks about using rel-alternate-hreflang in the following video.
The Language Targeting section of "International Targeting" in Webmaster Tools lets you identify missing return links and incorrect hreflang values.
Regarding missing return links, Google's Gary Illyes explains, "Annotations must be confirmed from the pages they are pointing to. If page A links to page B, page B must link back to page A, otherwise the annotations may not be interpreted correctly. For each error of this kind we report where and when we detected them, as well as where the return link is expected to be.
For incorrect hreflang values, he says, "The value of the hreflang attribute must either be a language code in ISO 639-1 format such as 'es', or a combination of language and country code such as 'es-AR', where the country code is in ISO 3166-1 Alpha 2 format. In case our indexing systems detect language or country codes that are not in these formats, we provide example URLs to help you fix them."
Google has also moved the geographic targeting setting to the International Targeting feature.
You can learn more about using rel-alternate-hreflang here.
Images via Google