gimp/README.i18n

This document exists to document the important things to care for
because of locale support. 
Actually this one is maintained by me, that is Daniel Egger 
(Daniel.Egger@t-online.de). 

1. Why localisation?

 Many persons from many countries start to get used to Linux.
 Unfortunately not everyone is able to understand English. But
 even those people some times like to use good software without
 needing a dictionary beneath them.
 So why not simply localise the software to make it available to 
 the mass which isn't wholly English native?

2. How?

 GNU provides a very nice package called gettext. This one offers
 the possibility to translate chosen messages from the native language
 of the program into that one of the users if a necessary catalog is
 provided. Gettext therefor provides some easy tools to create and maintain
 such catalogs and a few functions which can be called by the program to
 enable automatic translation. The program gets linked to gettext and
 everything is fine.
 By the way: gettext is a fixed part of glibc2 but will be shipped with
 GIMP and so can be automatically compiled on every platform GIMP itself
 runs on.

3. Deep inside...

 GIMP provides a header file called gimpintl.h in the libgimp directory this
 one checks whether gettext is available on the system and will deactivate
 language support if it's not.
 If it is useable it will define 3 functions which will be described below.

3.1 _() [more correctly: char * _( char * )]

 This one is a macro for the function gettext(). With it every text may be 
 wrapped that is directly called directly in a function. If you use it the
 given string will be tried to get translated in the native language of the
 user according to his/her environmental settings. 
 The gettext function will do a lookup in the hashed gimp.mo which contains 
 all the translated texts.

 - If it is found a pointer to the string will be returned to the caller.
 - If not the caller will receive a pointer to the original string.

 This way it is ensured that there isn't any harm caused to the program 
 (i.e. The GIMP) if no catalog isn't installed. 

 Please note that it is important to use _() directly (and not gettext())
 for simple messages because of reasons that will be mentioned below.

3.2 N_() [more correctly: void ( void ) ]

 This one is a macro for the function gettext_noop(). As you can see and
 guess it doesn't really anything in the programm i.e. it is a dummy
 function but nevertheless important. As it isn't possible to call functions
 in a structure as seen here:

 struct blurb
 {
  _("This won't work\n");
 }

 you have to do it in some other way. In GIMP such structures are often used 
 to create menues or similar things very simply. Here you have to use the
 dummy to allow the generation of a template which will be described below.
 This one doesn't do anything but it marks the text as important to the 
 gettext extractor.

 The text has to be translated "by hand" with the next function.  
 
3.3 gettext()

 This function is the same as that mcaro in 3.1. But there is one big
 difference: It is ignored by the gettext program which will create message
 templates for us. 
 If you have strings that should be translated but are unfortunately in a
 structure you have to do that on your own which means that you have to
 parse the fields with the messages in a loop and translate the texts with
 this gettext() function.

 Please note that it may be necessary to free or allocate memory in this
 case!      

4. Some magic...

 As you have seen we only did the programming part until now but this isn't
 all by far. 
 To use catalogs we'll have to create them. Now there are 3 different files
 which are importart:

 gimp.pot:
 
 This one is the so called template. It contains the messages which are
 extracted from the sources and empty fields which have to get filled by the
 author. It is used to start a new catalog or to update the an already
 available one. 

 The Makefile will automatically call the program gettext which will extract
 all messages that are wrapped by a _() or a N_() (but NOT gettext()) and
 concat them to this template.

 [language].po: 

 This file has to be an edited gimp.pot and contains the original messages 
 plus the translated ones. This file will be delivered together with GIMP
 and is the base for the final catalog.

 [language].mo:

 This file is a compiled version of [language.po] which will be
 automatically compiled by the Makefile and installed in the locale
 directory of the system. It contains everything that the .po file
 contains except not translated messages, comments and other overhead.
 For maximum speed it is also hashed to allow gettext a faster search.

5. Tools and how to use them...

 As mentioned the to get translated string are extracted directly from the
 source and written to the template. 
 I guess many of you will now ask if it is necessary to add new strings
 directly from the template or if there's a tool to achieve that. 
 I think I can calm down those one who fear of lots of had work just to
 update the language files. There's a program called msgmerge which will 
 add all strings that are in the template but not in the uncompiled catalog 
 to it. Msgmerge does this job very nicely and also tries to apply some kind
 of fuzzy search method for already translated string for possible
 programmers work reduction: If a original string seems similar to a new one 
 and it already has a translation, it will be taken over to the new catalog
 together with a remark that this one mustn't necessarily fit.
 
6. And more?

 I hope I mentioned everything that is worth it and hope that this document
 will clarify some things. If it doesn't please write me a mail and tell me
 what you want to know. This text may contain errors, so if you find one
 tell it to me, too....

Happy Gimping. Yours,
                     Daniel Egger