See how to change the language of a SharePoint team site with this end user SharePoint Tutorial. This affects e.g. the site settings but doesn't include content.
Multi-language installations are quite common in countries like Switzerland were people speak 4 different official languages (plus English): German, French, Italian and Romansh language. This doesn't affect only content user are creating... it affects also the SharePoint site they are using.
SharePoint MUI (multilingual user interface)
SharePoint 2010 supports a multilingual user interface for e.g. Team Sites. This includes application content, such as menus, controls, site actions, site title and description. This doesn't include user created content, such as list item data, documents and Web pages in libraries.
Blog templates and Meeting Workspace templates don't support a SharePoint multilingual user interface.
How to change language settings of a SharePoint site
Before you can change the language of a SharePoint site an administrator needs to install language packs on the SharePoint server. After they are installed and deployed you can go to site settings and language settings to enable a new language. If you click on your log-on name on the top right you can select a different language.
Learn more about SharePoint Language settings
Here you go: