Alphabet Soup: The Internationalization of Linux, Part 2

Mr. Turnbull takes a look at the problems faced with different character sets and the need for standardization.

A large body of standards has evolved to handle the problems with text manipulation I presented last month. In general, ad hoc handling methods are considered to be localization, while a method that conforms to some standard and is generalizable to many cultural environments is considered internationalization.

POSIX

Currently, the central standard for internationalization is the locale model of POSIX. Unfortunately, in the current state of the art, localization via the POSIX model is something of a Procrustean bed. For example, in Japanese there are two common ways of notating the currency unit yen: postfixing ¥ and prefixing &yen. It is not uncommon for both conventions to be used in the same document in different contexts: the former is common in running text, the latter in tables. POSIX does not provide for this. It is easy enough to implement by creating a Japanese-table locale to complement the Japanese-text locale, but this places the burden of setting the correct locale on the application programmer. Although much smaller in scale, this burden is much like that imposed by multilingualization. Nor was POSIX designed to support such fine discrimination; this is better left to the individual application anyway.

POSIX-style internationalization provides a comfortable, functional environment for almost all users and applications. Specifically, a POSIX locale determines:

  • the character set and encoding to be used

  • classification of characters (e.g., alpha, hex-digit, whitespace, etc.)

  • the sorting order for strings in the language

  • digit separator and decimal-point conventions

  • date and time presentation

  • currency presentation

  • message format (in particular, strings for yes and no)

All of these features are implemented by changing the functionality of standard library functions or by adding new ones. That is, the isalpha function in libc no longer consults a fixed table, but instead the table is varied according to the current locale. Displaying monetary values can be done by using the new function strfmon. Unfortunately, the locale support in Linux libc is still only partially documented as of libc-2.0.7t; no man page for strfmon exists, although there is an entry point in the library. A useful discussion by Ulrich Drepper, one of the authors of GNU libc, may be found at http://i44s11.info.uni-karlsruhe.de/~drepper/conf96/paper.html.

POSIX Internationalization Levels

The POSIX standard defines a number of levels of compliance with internationalization standards. These levels are a somewhat useful guide to how far an internationalization effort has progressed. Level 1 compliance is achieved when a system is 8-bit clean. Obviously this is a bare minimum, since some characters may get corrupted. Level 2 compliance is achieved when a flexible system for producing localized time, date and monetary formats is implemented. As described above, these facilities are provided by GNU libc, so disciplined use of appropriate formatting functions and the setlocale call is going to be sufficient for most applications to achieve Level 2 compliance. Level 3 compliance is achieved when the application can use localized message catalogs. This facility is provided by the GNU gettext library. Controlling gettext is nearly as simple as setting the locale. Unfortunately, the rules of precedence are somewhat different. However, disciplined use of gettext and its supporting functions will make localization much easier. (See “Internationalizing Messages in Linux Programs” by Pancrazio de Mauro, March 1999.)

Level 4 refers to Asian language support. The Asian languages are given a special status because of the variety of complex subsystems needed to support them. For example, many implementations of X have two separate families of string display functions, one for strings encoded in one byte and another for strings composed of characters encoded in two bytes. In Japanese, one- and two-byte characters are mixed freely, so an internationalized application which needs to deal with Japanese would have to analyze strings into one-byte and two-byte substrings on the fly. In fact, dealing with Japanese by itself forces the programmer to deal with many of the problems posed by true multilingual applications.

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