A system and method that simulate a system locale for non-Unicode application programs having languages that do not correspond to the system locale, to appropriately convert text data via a character set according to the application's native language. A shim mechanism converts the data in a program's relevant function calls based on a character set codepage for the program that corresponds to the program's language. The conversion is performed on a program-by-program basis, whereby multiple programs can properly execute simultaneously, even when programs have different languages and thus different character set codepages. Automatic language detection is provided, when possible, to determine the appropriate system locale to simulate via a corresponding codepage table. A user interface in the form of a wizard is provided to associate selected script-dependent applications with the needed conversion information, and/or to manually receive a language when automatic detection is unsuccessful.