Locale (computer software)

Locale (computer software)
In computing, a locale is a set of parameters that defines the user's language, region and any special variant preferences that the user wants to see in their user interface. Usually a locale identifier consists of at least a language code and a country/region code.
Locale is an important aspect of i18n.
General locale settings
These settings usually include the following display (output) format settings:
Number format setting (LC_NUMERIC, C/C++)
Character classification, case conversion settings (LC_CTYPE, C/C++)
Date-time format setting (LC_TIME, C/C++)
String collation setting (LC_COLLATE, C/C++)
Currency format setting (LC_MONETARY, C/C++)
Paper size setting (LC_PAPER, ISO 30112)
Color setting
The locale settings are about formatting output given a locale. So, the time zone information and daylight saving time are not usually part of the locale settings.
Less usual is the input format setting, which is mostly defined on a per application basis.
Programming and markup language support
In these environments,
C
C++
Eiffel
Java
.NET Framework
REBOL
Ruby
Perl
PHP
Python
XML
JSP
JavaScript
and other (nowadays) Unicode-based environments, they are defined in a format similar to BCP 47. They are usually defined with just ISO 639 (language) and ISO 3166-1 alpha-2 (2-letter country) codes.
International standards
In standard C and C++, locale is defined in "categories" of (text collation), (character class), (currency format), (number format), and (time format). The special category can be used to set all locale settings.
There is no standard locale names associated with C and C++ standards besides a "minimal locale" name "C", although the POSIX format is a commonly-used baseline.
POSIX platforms
On POSIX platforms such as Unix, Linux and others, locale identifiers are defined in a way similar to the BCP 47 definition of language tags, but the locale variant modifier is defined differently, and the character set is optionally included as a part of the identifier. The POSIX or "XPG" format is . (For example, Australian English using the UTF-8 encoding is .) Separately, ISO/IEC 15897 describes a different form though it's highly dubious whether it is used at all.
In the next example there is an output of command locale for Czech language (cs), Czech Republic (CZ) with explicit UTF-8 encoding:
$ locale
LANG=cs_CZ.UTF-8
LC_CTYPE="cs_CZ.UTF-8"
LC_NUMERIC="cs_CZ.UTF-8"
LC_TIME="cs_CZ.UTF-8"
LC_COLLATE="cs_CZ.UTF-8"
LC_MONETARY="cs_CZ.UTF-8"
LC_MESSAGES="cs_CZ.UTF-8"
LC_PAPER="cs_CZ.UTF-8"
LC_NAME="cs_CZ.UTF-8"
LC_ADDRESS="cs_CZ.UTF-8"
LC_TELEPHONE="cs_CZ.UTF-8"
LC_MEASUREMENT="cs_CZ.UTF-8"
LC_IDENTIFICATION="cs_CZ.UTF-8"
LC_ALL=
Specifics for Microsoft platforms
Windows uses specific language and territory strings.
The locale identifier (LCID) for unmanaged code on Microsoft Windows is a number such as 1033 for English (United States) or 1041 for Japanese (Japan). These numbers consist of a language code (lower 10 bits) and a culture code (upper bits), and are therefore often written in hexadecimal notation, such as 0x0409 or 0x0411.
Microsoft is starting to introduce managed code application programming interfaces (APIs) for .NET that use this format. One of the first to be generally released is a function to mitigate issues with internationalized domain names, but more are in Windows Vista Beta 1.
Starting with Windows Vista, new functions that use BCP 47 locale names have been introduced to replace nearly all LCID-based APIs.
A POSIX-like locale name format of is available in the UCRT (Universal C Run Time) of Windows 10 and 11.
See also
Internationalization and localization
ISO 639 language codes
ISO 3166-1 alpha-2 region codes
ISO 15924 script codes
IETF language tag
C localization functions
CCSID
Code page
Common Locale Data Repository
Date and time representation by country
AppLocale
References
External links
BCP 47
Language Subtag Registry
Common Locale Data Repository
Javadoc API documentation
Locale and Language information from Microsoft
MS-LCID: Windows Language Code Identifier (LCID) Reference from Microsoft
Microsoft LCID list
Microsoft LCID chart with decimal equivalents
POSIX Environment Variables
Low Level Technical details on defining a POSIX locale
ICU Locale Explorer
Debian Wiki on Locales
Article "The Standard C++ Locale" by Nathan C. Myers
locale(7): Description of multi-language support - Linux man page
Apache C++ Standard Library Locale User's Guide
Sort order charts for various operating system locales and database collations
NATSPEC Library
Description of locale-related UNIX environment variables in Debian Linux Reference Manual
Guides to locales and locale creation on various platforms
Unix user management and support-related utilities
Unix SUS2008 utilities
Internationalization and localization