In order to configure a different language for your store, you have to download the language package from the MagentoConnect Web Site: http://www.magentocommerce.com/magento-connect
There you can search and find your desired language.
1) Choose the language you want, then click in “Get extension key” and copy the line.
2)In your admin, go to System → Magento Connect → Magento Connect Manager, paste the extension key and click “Install”.
3)Click on “Return to Admin”. Under “Current Configuration Scope:” select the language you want to configure, for example “German”:
4) Now click in “General” tab, then select “Locale Options”, in “Locale” field select the language, like this:
That’s it. The language you selected will be assigned in the selected store-view. You would also have to assign a Homepage and static-blocks to this store-view.
Be sure to clear the cache before trying to use your new language.
You will have to do this same procedure with every language you want to set up for your store.-