In Microsoft terminology, a Language Interface Pack (LIP) is a skin for localizing a Windows operating system in languages such as Lithuanian, Serbian, Hindi, Marathi, Kannada, Tamil, and Thai.
Unlike MUI packs which are available only to Microsoft volume license customers and for specific SKUs of Windows Vista, a Language Interface Pack is available for free and can be installed on a licensed copy of Microsoft Windows or Office and a fixed "base language".
In other words, if the desired additional language has incomplete localization, users may add it for free, while if the language has complete localization, the user must pay for it by licensing a premium version of Windows.
It is an intermediate localized solution that enables computer users to adapt their software to display many commonly used features in their native language.
Each new Language Interface Pack is built using the glossary created by the Community Glossary Project in cooperation with the local government, academia, and local linguistic experts.