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Internationalization
An application that can present information to users according to regional cultural conventions is said to be internationalized: The application can be configured to interact with users from different localities in culturally appropriate ways. In an internationalized application, a user in one region sees error messages, output, and interface elements in the requested language. Date and time formats, as well as currencies, are presented appropriately for users in the specified region. A user in another region sees output in the conventional language or format for that region.
Historically, the creation of internationalized applications has been restricted to large corporations writing complex systems. Internationalization techniques have traditionally been expensive and difficult to implement, so they have been applied only to major development efforts. However, given the rise in distributed computing and in the use of the World Wide Web, application developers have been pressured to internationalize a much wider variety of applications. This requires making internationalization techniques much more accessible to application developers.
In an application that is not internationalized, the interface that the user sees is unalterably written into the application code. On the other hand, localizing the displayed strings adds a layer of abstraction into the design of the application. Instead of simply printing an error message, an internationalized application represents the error message with some language-neutral information; in the simplest case, each error condition corresponds to a key. To print a usable error message, then, the application looks up the key in the configured message catalog. Each message catalog is a list of keys with associated strings. Different message catalogs provide strings for the different languages supported. The application looks up the key in the appropriate catalog, retrieves the corresponding error message in the requested language, and prints this string for the user.
Localization of text can be used for far more than translating error messages. For example, by using keys to represent each element in a graphical user interface (GUI) and by providing the appropriate message catalogs, the GUI itself (buttons, menus, and so on) can support multiple languages. Extending support to additional languages requires that you provide message catalogs for those languages; in many cases, the application itself needs no further modification.
Internationalization of an application is driven by two variables, the time zone and the locale. The time zone indicates how to compute the local time as an offset from a standard time like Greenwich Mean Time. The locale is a collection of information about language, currency, and the conventions for presenting information like dates. In a localized application, the locale also indicates the message catalog from which an application is to retrieve message strings. A time zone can cover many locales, and a single locale can span time zones. With both time zone and locale, the date, time, currency, and language for users in a specific region can be determined.
Internationalizing applications
Internationalization: Resources for learning