The following diagram summarizes the relation between the files
handled by GNU
gettext and the tools acting on these files.
It is followed by somewhat detailed explanations, which you should
read while keeping an eye on the diagram. Having a clear understanding
of these interrelations will surely help programmers, translators
Original C Sources ───> Preparation ───> Marked C Sources ───╮ │ ╭─────────<─── GNU gettext Library │ ╭─── make <───┤ │ │ ╰─────────<────────────────────┬───────────────╯ │ │ │ ╭─────<─── PACKAGE.pot <─── xgettext <───╯ ╭───<─── PO Compendium │ │ │ ↑ │ │ ╰───╮ │ │ ╰───╮ ├───> PO editor ───╮ │ ├────> msgmerge ──────> LANG.po ────>────────╯ │ │ ╭───╯ │ │ │ │ │ ╰─────────────<───────────────╮ │ │ ├─── New LANG.po <────────────────────╯ │ ╭─── LANG.gmo <─── msgfmt <───╯ │ │ │ ╰───> install ───> /.../LANG/PACKAGE.mo ───╮ │ ├───> "Hello world!" ╰───────> install ───> /.../bin/PROGRAM ───────╯
As a programmer, the first step to bringing GNU
into your package is identifying, right in the C sources, those strings
which are meant to be translatable, and those which are untranslatable.
This tedious job can be done a little more comfortably using emacs PO
mode, but you can use any means familiar to you for modifying your
C sources. Beside this some other simple, standard changes are needed to
properly initialize the translation library. See Preparing Program Sources, for
more information about all this.
For newly written software the strings of course can and should be
marked while writing it. The
gettext approach makes this
very easy. Simply put the following lines at the beginning of each file
or in a central header file:
#define _(String) (String) #define N_(String) String #define textdomain(Domain) #define bindtextdomain(Package, Directory)
Doing this allows you to prepare the sources for internationalization.
Later when you feel ready for the step to use the
simply replace these definitions by the following:
#include <libintl.h> #define _(String) gettext (String) #define gettext_noop(String) String #define N_(String) gettext_noop (String)
and link against libintl.a or libintl.so. Note that on
GNU systems, you don’t need to link with
libintl because the
gettext library functions are already contained in GNU libc.
That is all you have to change.
Once the C sources have been modified, the
is used to find and extract all translatable strings, and create a
PO template file out of all these. This package.pot file
contains all original program strings. It has sets of pointers to
exactly where in C sources each string is used. All translations
are set to empty. The letter
t in .pot marks this as
a Template PO file, not yet oriented towards any particular language.
See Invoking the
xgettext Program, for more details about how one calls the
xgettext program. If you are really lazy, you might
be interested at working a lot more right away, and preparing the
whole distribution setup (see The Maintainer’s View). By doing so, you
spare yourself typing the
xgettext command, as
should now generate the proper things automatically for you!
The first time through, there is no lang.po yet, so the
msgmerge step may be skipped and replaced by a mere copy of
package.pot to lang.po, where lang
represents the target language. See Creating a New PO File for details.
Then comes the initial translation of messages. Translation in itself is a whole matter, still exclusively meant for humans, and whose complexity far overwhelms the level of this manual. Nevertheless, a few hints are given in some other chapter of this manual (see The Translator’s View). You will also find there indications about how to contact translating teams, or becoming part of them, for sharing your translating concerns with others who target the same native language.
While adding the translated messages into the lang.po PO file, if you are not using one of the dedicated PO file editors (see Editing PO Files), you are on your own for ensuring that your efforts fully respect the PO file format, and quoting conventions (see The Format of PO Files). This is surely not an impossible task, as this is the way many people have handled PO files around 1995. On the other hand, by using a PO file editor, most details of PO file format are taken care of for you, but you have to acquire some familiarity with PO file editor itself.
If some common translations have already been saved into a compendium PO file, translators may use PO mode for initializing untranslated entries from the compendium, and also save selected translations into the compendium, updating it (see Using Translation Compendia). Compendium files are meant to be exchanged between members of a given translation team.
Programs, or packages of programs, are dynamic in nature: users write bug reports and suggestion for improvements, maintainers react by modifying programs in various ways. The fact that a package has already been internationalized should not make maintainers shy of adding new strings, or modifying strings already translated. They just do their job the best they can. For the Translation Project to work smoothly, it is important that maintainers do not carry translation concerns on their already loaded shoulders, and that translators be kept as free as possible of programming concerns.
The only concern maintainers should have is carefully marking new
strings as translatable, when they should be, and do not otherwise
worry about them being translated, as this will come in proper time.
Consequently, when programs and their strings are adjusted in various
ways by maintainers, and for matters usually unrelated to translation,
xgettext would construct package.pot files which are
evolving over time, so the translations carried by lang.po
are slowly fading out of date.
It is important for translators (and even maintainers) to understand that package translation is a continuous process in the lifetime of a package, and not something which is done once and for all at the start. After an initial burst of translation activity for a given package, interventions are needed once in a while, because here and there, translated entries become obsolete, and new untranslated entries appear, needing translation.
msgmerge program has the purpose of refreshing an already
existing lang.po file, by comparing it with a newer
package.pot template file, extracted by
out of recent C sources. The refreshing operation adjusts all
references to C source locations for strings, since these strings
move as programs are modified. Also,
msgmerge comments out as
obsolete, in lang.po, those already translated entries
which are no longer used in the program sources (see Obsolete Entries). It finally discovers new strings and inserts them in
the resulting PO file as untranslated entries (see Untranslated Entries). See Invoking the
msgmerge Program, for more information about what
msgmerge really does.
Whatever route or means taken, the goal is to obtain an updated lang.po file offering translations for all strings.
The temporal mobility, or fluidity of PO files, is an integral part of the translation game, and should be well understood, and accepted. People resisting it will have a hard time participating in the Translation Project, or will give a hard time to other participants! In particular, maintainers should relax and include all available official PO files in their distributions, even if these have not recently been updated, without exerting pressure on the translator teams to get the job done. The pressure should rather come from the community of users speaking a particular language, and maintainers should consider themselves fairly relieved of any concern about the adequacy of translation files. On the other hand, translators should reasonably try updating the PO files they are responsible for, while the package is undergoing pretest, prior to an official distribution.
Once the PO file is complete and dependable, the
is used for turning the PO file into a machine-oriented format, which
may yield efficient retrieval of translations by the programs of the
package, whenever needed at runtime (see The Format of GNU MO Files). See Invoking the
msgfmt Program, for more information about all modes of execution
Finally, the modified and marked C sources are compiled and linked
with the GNU
gettext library, usually through the operation of
make, given a suitable Makefile exists for the project,
and the resulting executable is installed somewhere users will find it.
The MO files themselves should also be properly installed. Given the
appropriate environment variables are set (see Setting the Locale through Environment Variables),
the program should localize itself automatically, whenever it executes.
The remainder of this manual has the purpose of explaining in depth the various steps outlined above.