You might want to display your web site in a different language. Writing the content in the chosen language will not be enough. The menu items and the standard messages should also be translated. This is a time consuming task.
However, the Joomla developers have thought about it and provided the support of different language packs.
Find the one for the chosen language. You can check at the following URL:
Make sure that it is compatible with Joomla 2.5.
Download it on your local computer and log in your Joomla 2.5 admin area. Navigate to Extensions -> Extension Manager. Click on the Browse button, find the language pack’s archive file and click on Upload & Install.
Once the language is installed you can make it the default for your web site from theExtensions -> Language Manager area.