Joomla! installs in English, but translations of the interfaces, sample data and help screens are available in dozens of languages. Help
If there is no language pack available for your language, instructions are available for creating your own translation, which you can also contribute to the community by starting a translation team to create an accredited translation.
Translations of the interfaces are installed using the extensions manager in the site administrator and then managed using the language manager.
If you have two or more languages installed you may enable the language switcher plugin and module. They should always be used together. If you create multilingual content and mark your content, menu items or modules as in specific languages and follow the complete instructions your users will be able to select a specific content language using the module. By default both the plugin and module are disabled.
There are a number of extensions that can help you manage translations of content available in the Joomla! Extensions Directory.