Windows NT is available in localized editions of many different languages, but the U.S. English edition can also be used to run applications written in other languages. This is true even when the base character sets are different, such as when applications are written in the Central and Eastern European languages, or in Greek. These applications require a user interface (UI) with dialog boxes, icons, and applets that provide information in the application's language, which may be different than the language being used in the current Windows NT UI.
To enable the U.S. English Windows NT user interface, as well as characters outside the Windows character set for the US and Western Europe (code page 1252), to display correctly within applications and in system edit controls, Windows NT uses intelligent font switching based on the currently selected locale. This allows currently shipping localized applications to run on the U.S. English version of Windows NT without modifying the application in any way.
An example of the problem being addressed here is that the U.S. English Windows NT shell font is MS Sans Serif but the shell font for Greek Windows 3.1 is MS Sans Serif Greek. These character sets cannot be directly mapped to each other so simply replacing the MS Sans Serif font with the MS Sans Serif Greek font when the locale is set to Greek does not allow existing applications with this kind of difference to run adequately or to display Greek characters in system menus, dialogs and edit controls. To resolve this problem at run time, Microsoft has defined a new font face name, MS Shell Dlg. It is mapped by an entry in the registry to the appropriate shell font for the currently active locale.