Download Languages :
http://www.magentocommerce.com/translations
1. download language files and place them into the right folders (app >design >frontend >default >default >local)
2. Login to admin panel and go to System > Manage stores
3. Create a new store view or modify
4. Now go to: Configuration -> Current Configuration Scope (Select your language from the dropdown) and on the right side under “Locale options” choose the desired language.
5. Clear the cache (System – Cache Management)
Now go to: Configuration -> Current Configuration Scope (Select your language from the dropdown) and on the right side under “Locale options” choose the desired language.