(libc.info)Message Translation


Message Translation
*******************

   The program's interface with the human should be designed in a way to
ease the human the task.  One of the possibilities is to use messages in
whatever language the user prefers.

   Printing messages in different languages can be implemented in
different ways.  One could add all the different languages in the
source code and add among the variants every time a message has to be
printed.  This is certainly no good solution since extending the set of
languages is difficult (the code must be changed) and the code itself
can become really big with dozens of message sets.

   A better solution is to keep the message sets for each language are
kept in separate files which are loaded at runtime depending on the
language selection of the user.

   The GNU C Library provides two different sets of functions to support
message translation.  The problem is that neither of the interfaces is
officially defined by the POSIX standard.  The `catgets' family of
functions is defined in the X/Open standard but this is derived from
industry decisions and therefore not necessarily based on reasonable
decisions.

   As mentioned above the message catalog handling provides easy
extendibility by using external data files which contain the message
translations.  I.e., these files contain for each of the messages used
in the program a translation for the appropriate language.  So the tasks
of the message handling functions are

   * locate the external data file with the appropriate translations.

   * load the data and make it possible to address the messages

   * map a given key to the translated message

   The two approaches mainly differ in the implementation of this last
step.  The design decisions made for this influences the whole rest.

Message catalogs a la X/Open: The `catgets' family of functions.
The Uniforum approach: The `gettext' family of functions.

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