Localizing the Language Displayed by Dialogs
The Windows Installer service uses the current user's language in all dialogs until a Windows Installer package is opened. The Windows Installer determines this by using GetUserDefaultUILanguage. When a Windows Installer package is opened, the installer displays dialogs using the package's language as specified by the Template Summary Property.
For more information about localizing the language of a Windows Installer package, see also A Localization Example.