The Windows XP MUI (Multilingual User Interface) Pack, often referred to as mui pack or windows xp mui pack pl exe , is a software package developed by Microsoft to provide a multilingual user interface for Windows XP operating systems. Released in 2002, the MUI Pack allowed users to switch between different languages on a Windows XP system, making it a valuable tool for global businesses, organizations, and individuals who needed to use the operating system in multiple languages.