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45.2. For the Programmer

45.2.1. Mechanics

This section describes how to implement native language support in a program or library that is part of the PostgreSQL distribution. Currently, it only applies to C programs.

Adding NLS support to a program

  1. Insert this code into the start-up sequence of the program:

    #ifdef ENABLE_NLS
    #include <locale.h>
    #endif
    
    ...
    
    #ifdef ENABLE_NLS
    setlocale(LC_ALL, "");
    bindtextdomain("progname", LOCALEDIR);
    textdomain("progname");
    #endif
    

    (The progname can actually be chosen freely.)

  2. Wherever a message that is a candidate for translation is found, a call to gettext() needs to be inserted. E.g.,

    fprintf(stderr, "panic level %d\n", lvl);
    

    would be changed to

    fprintf(stderr, gettext("panic level %d\n"), lvl);
    

    (gettext is defined as a no-op if no NLS is configured.)

    This may tend to add a lot of clutter. One common shortcut is to use

    #define _(x) gettext(x)
    

    Another solution is feasible if the program does much of its communication through one or a few functions, such as ereport() in the backend. Then you make this function call gettext internally on all input strings.

  3. Add a file nls.mk in the directory with the program sources. This file will be read as a makefile. The following variable assignments need to be made here:

    CATALOG_NAME

    The program name, as provided in the textdomain() call.

    AVAIL_LANGUAGES

    List of provided translations — initially empty.

    GETTEXT_FILES

    List of files that contain translatable strings, i.e., those marked with gettext or an alternative solution. Eventually, this will include nearly all source files of the program. If this list gets too long you can make the first "file" be a + and the second word be a file that contains one file name per line.

    GETTEXT_TRIGGERS

    The tools that generate message catalogs for the translators to work on need to know what function calls contain translatable strings. By default, only gettext() calls are known. If you used _ or other identifiers you need to list them here. If the translatable string is not the first argument, the item needs to be of the form func:2 (for the second argument).

The build system will automatically take care of building and installing the message catalogs.

45.2.2. Message-writing guidelines

Here are some guidelines for writing messages that are easily translatable.

  • Do not construct sentences at run-time, like

    printf("Files were %s.\n", flag ? "copied" : "removed");
    

    The word order within the sentence may be different in other languages. Also, even if you remember to call gettext() on each fragment, the fragments may not translate well separately. It's better to duplicate a little code so that each message to be translated is a coherent whole. Only numbers, file names, and such-like run-time variables should be inserted at run time into a message text.

  • For similar reasons, this won't work:

    printf("copied %d file%s", n, n!=1 ? "s" : "");
    

    because it assumes how the plural is formed. If you figured you could solve it like this

    if (n==1)
        printf("copied 1 file");
    else
        printf("copied %d files", n):
    

    then be disappointed. Some languages have more than two forms, with some peculiar rules. We may have a solution for this in the future, but for now the matter is best avoided altogether. You could write:

    printf("number of copied files: %d", n);
    
  • If you want to communicate something to the translator, such as about how a message is intended to line up with other output, precede the occurrence of the string with a comment that starts with translator, e.g.,

    /* translator: This message is not what it seems to be. */
    

    These comments are copied to the message catalog files so that the translators can see them.

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