LCIDs

LCIDs, or Locale Identifiers, are numeric values used by Windows to identify a specific locale—combining language, regional settings, and often sorting rules—for the purpose of formatting data, selecting resources, and other culture-specific behavior. An LCID is a 32-bit value in Windows APIs; the low 16 bits encode a language ID and a sublanguage identifying the locale, while the higher bits may carry additional sort order or reserved data. The LANGID part can be constructed with macros such as MAKELANGID and SUBLANG constants in development.

Common examples include 0x0409 for English (United States), 0x0407 for German (Germany), and 0x040C for French (France). These values are used by functions such as GetUserDefaultLCID, GetThreadLocale, and SetThreadLocale to tailor formatting (dates, numbers, currency), string resources, and input behavior to the user's locale.

LCIDs are largely Windows-specific and have historically been used for resource loading by language-specific resource DLLs and for locale-aware API calls. They coexist with locale names or language tags (like en-US) in modern software; some APIs accept either form, while others prefer or require LCIDs for compatibility with older code.

In practice, developers may need to map between LCIDs and human-readable names, or convert to BCP 47 language tags for cross-platform interoperability. Understanding LCIDs is useful when dealing with legacy Windows applications, internationalization, and locale-sensitive operations in the Windows API.