Multilanguage User Interface Pack

MUI FAQ
Windows Server 2003, Windows XP, and Windows 2000 MUI
Multilingual User Interface Pack is a set of language specific resource files that can be added to the English version of Windows Professional. When installed on the English version of Windows, MUI allows the user interface language of the operating system to be changed according to the preferences of individual users to one of the 33 supported languages. This allows large corporations to roll out the same worldwide image with a single install job. Local users can then select the user interface language or it can be set by Group Policy for Organizational Units.

MUI also allows different language users to share the same workstation or roaming users to take their localized user interface from one workstation to another. For instance, one user might choose to see system menus, dialogs and other text in Japanese, while another user logging onto the same system might prefer to see the corresponding text in French

Microsoft first introduced the Multilingual User Interface Technology for Windows 2000 Professional as "Windows 2000 Professional Multilanguage Version," which was later extended to the Windows 2000 Server family. This technology is now available for Windows XP Professional, Windows Server 2003 editions, Windows XP Embedded, and Windows XP Tablet PC Edition. This technology is now called Multilingual User Interface Pack, referred to as MUI.
How to: Perform an unattended install of the Windows MUI
http://www.microsoft.com/globaldev/reference/win2k/setup/unattended.mspx