GNU gettext utilities: 1. Introduction

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# 1. Introduction

This chapter explains the goals sought in the creation of GNU `gettext` and the free Translation Project. Then, it explains a few broad concepts around Native Language Support, and positions message translation with regard to other aspects of national and cultural variance, as they apply to programs. It also surveys those files used to convey the translations. It explains how the various tools interact in the initial generation of these files, and later, how the maintenance cycle should usually operate.

In this manual, we use he when speaking of the programmer or maintainer, she when speaking of the translator, and they when speaking of the installers or end users of the translated program. This is only a convenience for clarifying the documentation. It is absolutely not meant to imply that some roles are more appropriate to males or females. Besides, as you might guess, GNU `gettext` is meant to be useful for people using computers, whatever their sex, race, religion or nationality!

Please submit suggestions and corrections

- either in the bug tracker at https://savannah.gnu.org/projects/gettext
- or by email to `bug-gettext@gnu.org`.

Please include the manual's edition number and update date in your messages.

## 1.1 The Purpose of GNU `gettext`

Usually, programs are written and documented in English, and use English at execution time to interact with users. This is true not only of GNU software, but also of a great deal of proprietary and free software. Using a common language is quite handy for communication between developers, maintainers and users from all countries. On the other hand, most people are less comfortable with English than with their own native language, and would prefer to use their mother tongue for day to day's work, as far as possible. Many would simply love to see their computer screen showing a lot less of English, and far more of their own language.

However, to many people, this dream might appear so far fetched that they may believe it is not even worth spending time thinking about it. They have no confidence at all that the dream might ever become true. Yet some have not lost hope, and have organized themselves. The Translation Project is a formalization of this hope into a workable structure, which has a good chance to get all of us nearer the achievement of a truly multi-lingual set of programs.

GNU `gettext` is an important step for the Translation Project, as it is an asset on which we may build many other steps. This package offers to programmers, translators and even users, a well integrated set of tools and documentation. Specifically, the GNU `gettext` utilities are a set of tools that provides a framework within which other free packages may produce multi-lingual messages. These tools include

- A set of conventions about how programs should be written to support message catalogs.
- A directory and file naming organization for the message catalogs themselves.
- A runtime library supporting the retrieval of translated messages.
- A few stand-alone programs to massage in various ways the sets of translatable strings, or already translated strings.
- A library supporting the parsing and creation of files containing translated messages.
- A special mode for Emacs(1) which helps preparing these sets and bringing them up to date.

GNU `gettext` is designed to minimize the impact of internationalization on program sources, keeping this impact as small and hardly noticeable as possible. Internationalization has better chances of succeeding if it is very light weighted, or at least, appear to be so, when looking at program sources.

The Translation Project also uses the GNU `gettext` distribution as a vehicle for documenting its structure and methods. This goes beyond the strict technicalities of documenting the GNU `gettext` proper. By so doing, translators will find in a single place, as far as possible, all they need to know for properly doing their translating work. Also, this supplemental documentation might also help programmers, and even curious users, in understanding how GNU `gettext` is related to the remainder of the Translation Project, and consequently, have a glimpse at the big picture.

## 1.2 I18n, L10n, and Such

Two long words appear all the time when we discuss support of native language in programs, and these words have a precise meaning, worth being explained here, once and for all in this document. The words are internationalization and localization. Many people, tired of writing these long words over and over again, took the habit of writing i18n and l10n instead, quoting the first and last letter of each word, and replacing the run of intermediate letters by a number merely telling how many such letters there are. But in this manual, in the sake of clarity, we will patiently write the names in full, each time…

By internationalization, one refers to the operation by which a program, or a set of programs turned into a package, is made aware of and able to support multiple languages. This is a generalization process, by which the programs are untied from calling only English strings or other English specific habits, and connected to generic ways of doing the same, instead. Program developers may use various techniques to internationalize their programs. Some of these have been standardized. GNU `gettext` offers one of these standards. See section The Programmer's View.

By localization, one means the operation by which, in a set of programs already internationalized, one gives the program all needed information so that it can adapt itself to handle its input and output in a fashion which is correct for some native language and cultural habits. This is a particularisation process, by which generic methods already implemented in an internationalized program are used in specific ways. The programming environment puts several functions to the programmers disposal which allow this runtime configuration. The formal description of specific set of cultural habits for some country, together with all associated translations targeted to the same native language, is called the locale for this language or country. Users achieve localization of programs by setting proper values to special environment variables, prior to executing those programs, identifying which locale should be used.

In fact, locale message support is only one component of the cultural data that makes up a particular locale. There are a whole host of routines and functions provided to aid programmers in developing internationalized software and which allow them to access the data stored in a particular locale. When someone presently refers to a particular locale, they are obviously referring to the data stored within that particular locale. Similarly, if a programmer is referring to “accessing the locale routines”, they are referring to the complete suite of routines that access all of the locale's information.

One uses the expression Native Language Support, or merely NLS, for speaking of the overall activity or feature encompassing both internationalization and localization, allowing for multi-lingual interactions in a program. In a nutshell, one could say that internationalization is the operation by which further localizations are made possible.

Also, very roughly said, when it comes to multi-lingual messages, internationalization is usually taken care of by programmers, and localization is usually taken care of by translators.

## 1.3 Aspects in Native Language Support

For a totally multi-lingual distribution, there are many things to translate beyond output messages.

- As of today, GNU `gettext` offers a complete toolset for translating messages output by C programs. Perl scripts and shell scripts will also need to be translated. Even if there are today some hooks by which this can be done, these hooks are not integrated as well as they should be.
- Some programs, like `autoconf` or `bison`, are able to produce other programs (or scripts). Even if the generating programs themselves are internationalized, the generated programs they produce may need internationalization on their own, and this indirect internationalization could be automated right from the generating program. In fact, quite usually, generating and generated programs could be internationalized independently, as the effort needed is fairly orthogonal.
- A few programs include textual tables which might need translation themselves, independently of the strings contained in the program itself. For example, RFC 1345 gives an English description for each character which the `recode` program is able to reconstruct at execution. Since these descriptions are extracted from the RFC by mechanical means, translating them properly would require a prior translation of the RFC itself.
- Almost all programs accept options, which are often worded out so to be descriptive for the English readers; one might want to consider offering translated versions for program options as well.
- Many programs read, interpret, compile, or are somewhat driven by input files which are texts containing keywords, identifiers, or replies which are inherently translatable. For example, one may want `gcc` to allow diacriticized characters in identifiers or use translated keywords; ‘`rm -i`’ might accept something else than ‘`y`’ or ‘`n`’ for replies, etc. Even if the program will eventually make most of its output in the foreign languages, one has to decide whether the input syntax, option values, etc., are to be localized or not.
- The manual accompanying a package, as well as all documentation files in the distribution, could surely be translated, too. Translating a manual, with the intent of later keeping up with updates, is a major undertaking in itself, generally.

As we already stressed, translation is only one aspect of locales. Other internationalization aspects are system services and are handled in GNU `libc`. There are many attributes that are needed to define a country's cultural conventions. These attributes include beside the country's native language, the formatting of the date and time, the representation of numbers, the symbols for currency, etc. These local rules are termed the country's locale. The locale represents the knowledge needed to support the country's native attributes.

There are a few major areas which may vary between countries and hence, define what a locale must describe. The following list helps putting multi-lingual messages into the proper context of other tasks related to locales. See the GNU `libc` manual for details.

Characters and Codesets

  The codeset most commonly used through out the USA and most English speaking parts of the world is the ASCII codeset. However, there are many characters needed by various locales that are not found within this codeset. The 8-bit ISO 8859-1 code set has most of the special characters needed to handle the major European languages. However, in many cases, choosing ISO 8859-1 is nevertheless not adequate: it doesn't even handle the major European currency. Hence each locale will need to specify which codeset they need to use and will need to have the appropriate character handling routines to cope with the codeset.

Currency

  The symbols used vary from country to country as does the position used by the symbol. Software needs to be able to transparently display currency figures in the native mode for each locale.

Dates

  The format of date varies between locales. For example, Christmas day in 1994 is written as 12/25/94 in the USA and as 25/12/94 in Australia. Other countries might use ISO 8601 dates, etc.

  Time of the day may be noted as hh:mm, hh.mm, or otherwise. Some locales require time to be specified in 24-hour mode rather than as AM or PM. Further, the nature and yearly extent of the Daylight Saving correction vary widely between countries.

Numbers

  Numbers can be represented differently in different locales. For example, the following numbers are all written correctly for their respective locales:

      12,345.67       English
      12.345,67       German
       12345,67       French
      1,2345.67       Asia

  Some programs could go further and use different unit systems, like English units or Metric units, or even take into account variants about how numbers are spelled in full.

Messages

  The most obvious area is the language support within a locale. This is where GNU `gettext` provides the means for developers and users to easily change the language that the software uses to communicate to the user.

These areas of cultural conventions are called locale categories. It is an unfortunate term; locale aspects or locale feature categories would be a better term, because each “locale category” describes an area or task that requires localization. The concrete data that describes the cultural conventions for such an area and for a particular culture is also called a locale category. In this sense, a locale is composed of several locale categories: the locale category describing the codeset, the locale category describing the formatting of numbers, the locale category containing the translated messages, and so on.

Components of locale outside of message handling are standardized in the ISO C standard and the POSIX:2001 standard (also known as the SUSV3 specification). GNU `libc` fully implements this, and most other modern systems provide a more or less reasonable support for at least some of the missing components.

## 1.4 Files Conveying Translations

The letters PO in ‘`.po`’ files means Portable Object, to distinguish it from ‘`.mo`’ files, where MO stands for Machine Object. This paradigm, as well as the PO file format, is inspired by the NLS standard developed by Uniforum, and first implemented by Sun in their Solaris system.

PO files are meant to be read and edited by humans, and associate each original, translatable string of a given package with its translation in a particular target language. A single PO file is dedicated to a single target language. If a package supports many languages, there is one such PO file per language supported, and each package has its own set of PO files. These PO files are best created by the `xgettext` program, and later updated or refreshed through the `msgmerge` program. Program `xgettext` extracts all marked messages from a set of C files and initializes a PO file with empty translations. Program `msgmerge` takes care of adjusting PO files between releases of the corresponding sources, commenting obsolete entries, initializing new ones, and updating all source line references. Files ending with ‘`.pot`’ are kind of base translation files found in distributions, in PO file format.

MO files are meant to be read by programs, and are binary in nature. A few systems already offer tools for creating and handling MO files as part of the Native Language Support coming with the system, but the format of these MO files is often different from system to system, and non-portable. The tools already provided with these systems don't support all the features of GNU `gettext`. Therefore GNU `gettext` uses its own format for MO files. Files ending with ‘`.gmo`’ are really MO files, when it is known that these files use the GNU format.

## 1.5 Overview of GNU `gettext`

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 and maintainers.

    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 `gettext` 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 section 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 `gettext` library 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 `xgettext` program 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 section 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 section The Maintainer's View). By doing so, you spare yourself typing the `xgettext` command, as `make` 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 section 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 section Editing PO Files), you are on your own for ensuring that your efforts fully respect the PO file format, and quoting conventions (see section 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 section 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.

The `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 `xgettext` 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 section Obsolete Entries). It finally discovers new strings and inserts them in the resulting PO file as untranslated entries (see section Untranslated Entries). See section 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 `msgfmt` program 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 section The Format of GNU MO Files). See section Invoking the `msgfmt` Program, for more information about all modes of execution for the `msgfmt` program.

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 section Setting the Locale through Environment Variables), the program should localize itself automatically, whenever it executes.

Shipping the MO files as separate files, as opposed to embedding them in the executable, has three advantages:

- For the users: It allows users to prepare and install new translations, without needing to rebuild the package (which may require developer skills).
- For the distributors: It allows distributions to ship translations that were produced after the release of the package.
- For the vendors of complex packages: When lengthy quality assurance steps are required before making a release, this quality assurance can start before the translators have produced the translations, shortening the critical path of the release schedule by a week or two.

Embedding the translations in the executable, whether by the ISO C `#embed` directive or through other means, would deprive users without developer skills of the ability to fix translation mistakes and add new translations.

The remainder of this manual has the purpose of explaining in depth the various steps outlined above.

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