I always find it interesting to share SEO questions submitted by huge brands and online properties. So when Shirin Oskooi, who I believes works at Yahoo currently but did work at Google and Microsoft asked a question on why Google was not picking up the international versions of Yahoo Answers properly, I became interested.
Shirin Oskooi said, "Google is sending all international traffic to the US version of Yahoo Answers as of September." She wanted to know why and Google's John Mueller said because the site is not using hreflang markup. That and Yahoo Answers USA undergoing a complete revamp, caused Google to confuse it all.
Shirin Oskooi added:
Yahoo specifies a canonical URL to send the user to the correct international version of Answers, but it's no longer being respected. What this means for users who click through to Answers is that they are seeing the Yahoo Answers Q&A content they intended to see, but the surroundings of the page are in US English as opposed to the language/content of their locale.
In September, Yahoo Answers launched a redesign to the US version of the site. Because the redesign is vastly different from the old site (which all international versions of the product still use), it's suspected that Google may think this is fundamentally different (and fresher) content.
Google's John Mueller explained:
This is something you could resolve by using the hreflang markup - so that we can recognize that these URLs are equivalent, and understand which one is the best one to show for the individual languages / locations.
So I guess between the new Yahoo Answers site, Google crawling it and not seeing the hreflang markup - it got confused.
Forum discussion at Google Webmaster Help.