Software that has been designed for internationalization is able to manage different linguistic and cultural conventions transparently and without modification. The same binary copy of an application should run on any localized version of an operating system without requiring source code changes.
Software that has been designed for localization includes language translation (such as text messages, icons, and buttons), cultural data (such as dates, times, and currency), and other components (such as input methods and spell checkers) for meeting regional market requirements.
Properly designed applications can accommodate a localized interface without extensive modification. The applications can be designed, first, to run internationally, and, second, to accommodate the language- and cultural-specific elements of a designated locale.
A locale represents the language and cultural data chosen by the user and dynamically loaded into memory at runtime. The locale settings are applied to the operating system and to subsequent application launches.
While language is a fairly straightforward item, cultural data is a little more complex. Dates, numbers, and currency are all examples of data that is formatted according to cultural expectations. Because cultural preferences are bound to a geographic area, country is an important element of locale. Together these two elements (language and country) provide a precise context in which information can be presented. Locale presents information in the language and form that is best understood and appreciated by the local user.
Because language is correlated with geography, a language code might not capture all the nuances of usage in a particular area. For example, French and Canadian French may use different phrases and terms to mean different things even though basic grammar and vocabulary are the same. Language is only one element of locale.
The locale's country identifier is also specified by an ISO standard, ISO 3166, which describes valid two-letter codes for all countries. ISO 3166 defines these codes in uppercase letters. The following table lists some commonly used country codes.
A variant is an optional extension to a locale. It identifies a custom locale that is not possible to create with just language and country codes. Variants can be used by anyone to add additional context for identifying a locale. The locale en_US represents English (United States), but en_US_CA represents even more information and might identify a locale for English (California, U.S.A). Operating system or software vendors can use these variants to create more descriptive locales for their specific environments.