Did you read what Google says about that issue?
Duplicate content and international sites
Websites that provide content for different regions and in different languages sometimes create content that is the same or similar but available on different URLs. This is generally not a problem as long as the content is for different users in different countries. While we strongly recommend that you provide unique content for each different group of users, we understand that this may not always be possible. There is generally no need to "hide" the duplicates by disallowing crawling in a robots.txt file or by using a "noindex" robots meta tag. However, if you're providing the same content to the same users on different URLs (for instance, if both example.de/ and example.com/de/ show German language content for users in Germany), you should pick a preferred version and redirect (or use therel=canonical link element) appropriately. In addition, you should follow the guidelines onrel-alternate-hreflang to make sure that the correct language or regional URL is served to searchers.

