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gettext: gettext grok

 
 11.5 Being a ‘gettext’ grok
 ===========================
 
    * NOTE: * This documentation section is outdated and needs to be
 revised.
 
    To fully exploit the functionality of the GNU ‘gettext’ library it is
 surely helpful to read the source code.  But for those who don’t want to
 spend that much time in reading the (sometimes complicated) code here is
 a list comments:
 
    • Changing the language at runtime
 
      For interactive programs it might be useful to offer a selection of
      the used language at runtime.  To understand how to do this one
      need to know how the used language is determined while executing
      the ‘gettext’ function.  The method which is presented here only
      works correctly with the GNU implementation of the ‘gettext’
      functions.
 
      In the function ‘dcgettext’ at every call the current setting of
      the highest priority environment variable is determined and used.
      Highest priority means here the following list with decreasing
      priority:
 
        1. ‘LANGUAGE’
        2. ‘LC_ALL’
        3. ‘LC_xxx’, according to selected locale category
        4. ‘LANG’
 
      Afterwards the path is constructed using the found value and the
      translation file is loaded if available.
 
      What happens now when the value for, say, ‘LANGUAGE’ changes?
      According to the process explained above the new value of this
      variable is found as soon as the ‘dcgettext’ function is called.
      But this also means the (perhaps) different message catalog file is
      loaded.  In other words: the used language is changed.
 
      But there is one little hook.  The code for gcc-2.7.0 and up
      provides some optimization.  This optimization normally prevents
      the calling of the ‘dcgettext’ function as long as no new catalog
      is loaded.  But if ‘dcgettext’ is not called the program also
      cannot find the ‘LANGUAGE’ variable be changed (⇒Optimized
      gettext).  A solution for this is very easy.  Include the
      following code in the language switching function.
 
             /* Change language.  */
             setenv ("LANGUAGE", "fr", 1);
 
             /* Make change known.  */
             {
               extern int  _nl_msg_cat_cntr;
               ++_nl_msg_cat_cntr;
             }
 
      The variable ‘_nl_msg_cat_cntr’ is defined in ‘loadmsgcat.c’.  You
      don’t need to know what this is for.  But it can be used to detect
      whether a ‘gettext’ implementation is GNU gettext and not non-GNU
      system’s native gettext implementation.
 

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