Adding multi-language support
The content management system Joomla! includes various language packs and translations for the user interface already. The combination of one specific language pack and the content in the same language allows you to build a website in any language you like.
If you build a website that should have more than one language you need some extensions for multi-lingual support. Those extensions will help you to maintain the translations as well as the organization of your content in the various languages.