If you’re planning to create one or several sites in different languages? You'll want to keep in mind factors like site structure, geographic as well as language targeting, and content organization. The first thing you'll consider is to buy country-specific TLDs for all the countries you plan to serve. But it can be pretty expensive to buy domains on the country-specific TLDs, and it's more of a pain to update and maintain multiple domains. So if your time and resources are limited, consider buying one non-country-specific domain, which hosts all the different versions of your website and use any of the following two options:
- Put the content of every language in a different subdomain. For our example, you would have en.example.com, de.example.com, and es.example.com.
- Put the content of every language in a different subdirectory. This is easier to handle when updating and maintaining your site. For our example, you would have example.com/en/, example.com/de/, and example.com/es/.
Matt Cutts wrote a substantial post on subdirectories and subdomains, which may help you decide which option to go with.
Geographic targeting vs. Language targeting: If your content is especially targeted towards a particular region in the world, you can use the Set Geographic Target tool in Webmaster Tools. It allows you to set different geographic targets for different subdirectories or subdomains (e.g., /de/ for Germany).
Content organization: The same content in different languages is not considered duplicate content. Avoid mixing languages on each page, as this may confuse Googlebot as well as your users. Keep navigation and content in the same language on each page. If you want to check how many of your pages are recognized in a certain language, you can perform a language-specific site search. For example, if you go to google.de and do a site search on google.com, choose the option below the search box to only display German results.
Source:→ Google Webmaster Central Blog