Recently, I wrote about domains and multilingual pages, it will not do any harm if we mention a few guidelines Google has issued on the blog. Shortly, if you plan to launch a multilingual site, it is important to pay attention to:
Site structure. First, think of the domain — decide between GeoTarget TLD model (e.g. local domains like .de for Germany, .it for Italy) or if your resources are limited, concentrate on the domain that is not specifical for certain market area and that will be used for all languages. In this case, there are two ways to do that:
Languages set on different subdomains. For example, de.page.com, it.page.com.
Each language set on different subdirectory. For example, page.com/de/, page.com/it/.
Geographic targeting vs. Language targeting. In case the content of your page is targeted at a certain region — it can be set using Google Webmaster Tools.
Content organization.Same content on different languages is NOT duplicate content. Make sure you organize such materials in the way that you avoid mixing language versions on the same page, which could be confusing for Googlebot and users.
As I said, shortly, that’s it, if you want to know more, read the official Google blog.