hreflang is markup you can add to your web sites to help communicate which URL Google should show in the search results for localized versions of Google. So if you have a UK site and a Germany site, you can communicate to Google to show the co.uk version in Google UK and the .de version in Google Germany.
But John Mueller of Google said it won't make your site rank better than it does without the hreflang. All it does is help Google know which URL to swap it out for based on the language or region of Google.
John Mueller said this on Friday in a hangout on Google+ at the 2:29 mark into the video. He said:
Kind of think think if you didn't have those local pages would the dot-com pages rank in the local search results? And if they would rank then we'd like to swap at the URLs out against the appropriate local versions. So if if you have a website, I don't know that, that's targeting furniture and you have a UK website and it doesn't show it all in in France for example, then just setting up at the href lang with completely new pages for France wouldn't change anything because we wouldn't have anything to swap out. It wouldn't be that your UK page would be excessively ranking.Another hand if you have liked for Germany and Austria where the the content is German both the same and your pages for the country of Germany happened to rank in Austria then that would be something that we could swap out.
So it doesn't seem it would rank any better, which I find interesting.
Here is the video embed so you can listen for yourself, it is the first question asked:
Forum discussion at Google+.
