Ubuntu in Your Language
When you installed Ubuntu, you were asked which language the system should use. Although this sets the initial language for the system, you may want to change the language at a later date. To do this, click System > Administration > Language Support.
Ubuntu supports a huge range of different languages, and many applications include a Translate This Application menu option in the Help menu so that all Ubuntu users can contribute translations in their language(s). If you would like to help with this effort, it is a fantastic contribution to the Ubuntu project.
When the language selector first loads, it may ask you to update your language packs. Just click Yes to continue. Inside the dialog box a number of languages are listed, each of which has a Support checkbox listed next to it. For each language that you want available on the system, check the relevant boxes.
When you have selected the boxes, click the Apply button, and the appropriate language packs are downloaded and installed. Now use the Default Language combo box to choose the new language. You need to log out and log back in for the changes to take effect.