Extracting Localized Text

Although there are different methods to localize an application, the general rule is that any language-dependent information is outside the application and is stored in separate directories identified by a locale name.

This section describes how the user, the application developer, and the implementation combine to establish the language environment of the application. Two general approaches to localizing applications are also discussed. The following three methods can be used:

• Resource files

• Message catalogs

• Private files

Resource Files

This is the GUI toolkit mechanism for customizing all sorts of information about an application. The Intrinsic library (libXt) provides a sophisticated mechanism for merging the command-line options, application-defined resources, and user-defined resources. Resource files can be used for extracting localized text. The difference between resource files and message catalogs is that the resource database is compiled each time it is loaded. As such, care should be taken when deciding which strings to place in resource files and which to place in message catalogs.

Also note that the Xm library functions do not depend on the LC_MESSAGE category when specifying the location from which localized resources are loaded. Refer to the XtSetLanguageProc() man page for more information.

Message Catalogs

This is the traditional operating system mechanism for accessing external databases containing localized text. These functions load a precompiled catalog file that is ready to be accessed. They also provide defaults within the actual program for cases when no catalogs may be found.

The messaging support is based on both the XPG4 and System V Release 4 (SVR4) interfaces for accessing message catalogs.

Private Files

Private databases can be used by applications to provide generic, customized databases for more than just localization text. Usually, such databases do contain text. It is recommended that if the database is to be spread out over many files, some run-time indirect access of localized text be provided. Without this access, localization for the average user is a difficult effort. Generally, such private file formats are discouraged by groups doing localization. But problems are reduced if a tool is provided specifically for localization of text only.