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# 4. Preparing Program Sources

For the programmer, changes to the C source code fall into three categories. First, you have to make the localization functions known to all modules needing message translation. Second, you should properly trigger the operation of GNU `gettext` when the program initializes, usually from the `main` function. Last, you should identify, adjust and mark all constant strings in your program needing translation.

## 4.1 Importing the `gettext` declaration

Presuming that your set of programs, or package, has been adjusted so all needed GNU `gettext` files are available, and your ‘`Makefile`’ files are adjusted (see section The Maintainer's View), each C module having translated C strings should contain the line:

    #include <libintl.h>

Similarly, each C module containing `printf()`/`fprintf()`/... calls with a format string that could be a translated C string (even if the C string comes from a different C module) should contain the line:

    #include <libintl.h>

## 4.2 Triggering `gettext` Operations

The initialization of locale data should be done with more or less the same code in every program, as demonstrated below:

    int
    main (int argc, char *argv[])
    {
      …
      setlocale (LC_ALL, "");
      bindtextdomain (PACKAGE, LOCALEDIR);
      textdomain (PACKAGE);
      …
    }

PACKAGE and LOCALEDIR should be provided either by ‘`config.h`’ or by the Makefile. For now consult the `gettext` or `hello` sources for more information.

The use of `LC_ALL` might not be appropriate for you. `LC_ALL` includes all locale categories and especially `LC_CTYPE`. This latter category is responsible for determining character classes with the `isalnum` etc. functions from ‘`ctype.h`’ which could especially for programs, which process some kind of input language, be wrong. For example this would mean that a source code using the ç (c-cedilla character) is runnable in France but not in the U.S.

Some systems also have problems with parsing numbers using the `scanf` functions if an other but the `LC_ALL` locale category is used. The standards say that additional formats but the one known in the `"C"` locale might be recognized. But some systems seem to reject numbers in the `"C"` locale format. In some situation, it might also be a problem with the notation itself which makes it impossible to recognize whether the number is in the `"C"` locale or the local format. This can happen if thousands separator characters are used. Some locales define this character according to the national conventions to `'.'` which is the same character used in the `"C"` locale to denote the decimal point.

So it is sometimes necessary to replace the `LC_ALL` line in the code above by a sequence of `setlocale` lines

    {
      …
      setlocale (LC_CTYPE, "");
      setlocale (LC_MESSAGES, "");
      …
    }

On all POSIX conformant systems the locale categories `LC_CTYPE`, `LC_MESSAGES`, `LC_COLLATE`, `LC_MONETARY`, `LC_NUMERIC`, and `LC_TIME` are available. On some systems which are only ISO C compliant, `LC_MESSAGES` is missing, but a substitute for it is defined in GNU gettext's `<libintl.h>` and in GNU gnulib's `<locale.h>`.

Note that changing the `LC_CTYPE` also affects the functions declared in the `<ctype.h>` standard header and some functions declared in the `<string.h>` and `<stdlib.h>` standard headers. If this is not desirable in your application (for example in a compiler's parser), you can use a set of substitute functions which hardwire the C locale, such as found in the modules ‘`c-ctype`’, ‘`c-strcase`’, ‘`c-strcasestr`’, ‘`c-snprintf`’, ‘`c-strtod`’, ‘`c-strtold`’, ‘`c-dtoastr`’, ‘`c-ldtoastr`’ in the GNU gnulib source distribution.

It is also possible to switch the locale forth and back between the environment dependent locale and the C locale, but this approach is normally avoided because a `setlocale` call is expensive, because it is tedious to determine the places where a locale switch is needed in a large program's source, and because switching a locale is not multithread-safe.

## 4.3 Preparing Translatable Strings

Before strings can be marked for translations, they sometimes need to be adjusted. Usually preparing a string for translation is done right before marking it, during the marking phase which is described in the next sections. What you have to keep in mind while doing that is the following.

- Decent English style.
- Entire sentences.
- Split at paragraphs.
- Use format strings instead of string concatenation.
- Use placeholders in format strings instead of embedded URLs.
- Use placeholders in format strings instead of programmer-defined format string directives.
- Avoid unusual markup and unusual control characters.

Let's look at some examples of these guidelines.

### 4.3.1 Decent English style

Translatable strings should be in good English style. If slang language with abbreviations and shortcuts is used, often translators will not understand the message and will produce very inappropriate translations.

    "%s: is parameter\n"

This is nearly untranslatable: Is the displayed item a parameter or the parameter?

    "No match"

The ambiguity in this message makes it unintelligible: Is the program attempting to set something on fire? Does it mean "The given object does not match the template"? Does it mean "The template does not fit for any of the objects"?

In both cases, adding more words to the message will help both the translator and the English speaking user.

### 4.3.2 Entire sentences

Translatable strings should be entire sentences. It is often not possible to translate single verbs or adjectives in a substitutable way.

    printf ("File %s is %s protected", filename, rw ? "write" : "read");

Most translators will not look at the source and will thus only see the string `"File %s is %s protected"`, which is unintelligible. Change this to

    printf (rw ? "File %s is write protected" : "File %s is read protected",
            filename);

This way the translator will not only understand the message, she will also be able to find the appropriate grammatical construction. A French translator for example translates "write protected" like "protected against writing".

Entire sentences are also important because in many languages, the declination of some word in a sentence depends on the gender or the number (singular/plural) of another part of the sentence. There are usually more interdependencies between words than in English. The consequence is that asking a translator to translate two half-sentences and then combining these two half-sentences through dumb string concatenation will not work, for many languages, even though it would work for English. That's why translators need to handle entire sentences.

Often sentences don't fit into a single line. If a sentence is output using two subsequent `printf` statements, like this

    printf ("Locale charset \"%s\" is different from\n", lcharset);
    printf ("input file charset \"%s\".\n", fcharset);

the translator would have to translate two half sentences, but nothing in the POT file would tell her that the two half sentences belong together. It is necessary to merge the two `printf` statements so that the translator can handle the entire sentence at once and decide at which place to insert a line break in the translation (if at all):

    printf ("Locale charset \"%s\" is different from\n\
    input file charset \"%s\".\n", lcharset, fcharset);

You may now ask: how about two or more adjacent sentences? Like in this case:

    puts ("Apollo 13 scenario: Stack overflow handling failed.");
    puts ("On the next stack overflow we will crash!!!");

Should these two statements merged into a single one? I would recommend to merge them if the two sentences are related to each other, because then it makes it easier for the translator to understand and translate both. On the other hand, if one of the two messages is a stereotypic one, occurring in other places as well, you will do a favour to the translator by not merging the two. (Identical messages occurring in several places are combined by `xgettext`, so the translator has to handle them once only.)

### 4.3.3 Split at paragraphs

Translatable strings should be limited to one paragraph; don't let a single message be longer than ten lines. The reason is that when the translatable string changes, the translator is faced with the task of updating the entire translated string. Maybe only a single word will have changed in the English string, but the translator doesn't see that (with the current translation tools), therefore she has to proofread the entire message.

Many GNU programs have a ‘`--help`’ output that extends over several screen pages. It is a courtesy towards the translators to split such a message into several ones of five to ten lines each. While doing that, you can also attempt to split the documented options into groups, such as the input options, the output options, and the informative output options. This will help every user to find the option he is looking for.

### 4.3.4 No string concatenation

Hardcoded string concatenation is sometimes used to construct English strings:

    strcpy (s, "Replace ");
    strcat (s, object1);
    strcat (s, " with ");
    strcat (s, object2);
    strcat (s, "?");

In order to present to the translator only entire sentences, and also because in some languages the translator might want to swap the order of `object1` and `object2`, it is necessary to change this to use a format string:

    sprintf (s, "Replace %s with %s?", object1, object2);

### String concatenation operator

In many programming languages, a particular operator denotes string concatenation at runtime (or possibly at compile time, if the compiler supports that).

- In C++, string concatenation of `std::string` objects is denoted by the ‘`+`’ operator.
- In Shell, string concatenation is denoted by mere juxtaposition of strings.
- In Python, string concatenation is denoted by the ‘`+`’ operator.
- In Smalltalk, string concatenation is denoted by the ‘`,`’ operator.
- In Java, string concatenation is denoted by the ‘`+`’ operator.
- In C#, string concatenation is denoted by the ‘`+`’ operator.
- In awk, string concatenation is denoted by mere juxtaposition of strings.
- In Perl, string concatenation is denoted by the ‘`.`’ operator.
- In PHP, string concatenation is denoted by the ‘`.`’ operator.
- In Ruby, string concatenation is denoted by the ‘`+`’ operator.
- In Lua, string concatenation is denoted by the ‘`..`’ operator.
- In JavaScript, string concatenation is denoted by the ‘`+`’ operator.
- In Vala, string concatenation is denoted by the ‘`+`’ operator.

So, for example, in Java, you would change

    System.out.println("Replace "+object1+" with "+object2+"?");

into a statement involving a format string:

    System.out.println(
        MessageFormat.format("Replace {0} with {1}?",
                             new Object[] { object1, object2 }));

Similarly, in C#, you would change

    Console.WriteLine("Replace "+object1+" with "+object2+"?");

into a statement involving a format string:

    Console.WriteLine(
        String.Format("Replace {0} with {1}?", object1, object2));

### Strings with embedded expressions

In some programming languages, it is possible to have strings with embedded expressions. The expressions can refer to variables of the program. The value of such an expression is converted to a string and inserted in place of the expression; but no formatting function is called.

- In Shell language, double-quoted strings can contain references to variables, along with default values and string operations. Such as `"Hello, $name!"` or `"Hello, ${name}!"`.
- In Python, f-strings can contain expressions. Such as `f"Hello, {name}!"`.
- In C#, since C# 6.0, interpolated strings can contain expressions. Such as `$"Hello, {name}!"`.
- In Tcl, strings are subject to variable substitution. Such as `"Hello, $name!"`.
- In Perl, interpolated strings can contain expressions. Such as `"Hello, $name!"`.
- In PHP, string literals are subject to variable parsing. Such as `"Hello, $name!"`.
- In Ruby, interpolated strings can contain expressions. Such as `"Hello, #{name}!"`.
- In JavaScript, since ES6, template literals can contain expressions. Such as ``Hello, ${name}!``.

These cases are effectively string concatenation as well, just with a different syntax.

So, for example, in Python, you would change

    print (f'Replace {object1.name} with {object2.name}?')

into a statement involving a format string:

    print ('Replace %(name1)s with %(name2)s?'
           % { 'name1': object1.name, 'name2': object2.name })

or equivalently

    print ('Replace {name1} with {name2}?'
           .format(name1 = object1.name, name2 = object2.name))

And in JavaScript, you would change

    print (`Replace ${object1.name} with ${object2.name}?`)

into a statement involving a format string:

    print ('Replace %s with %s?'.format(object1.name, object2.name))

Specifically in JavaScript, an alternative is to use a tagged template literal:

    print (tag`Replace ${object1.name} with ${object2.name}?`)

and pass an option ‘`--tag=tag:format`’ to `xgettext`.

### Format strings with embedded named references

Format strings with embedded named references are different: They are suitable for internationalization, because it is possible to insert a call to the `gettext` function (that will return a translated format string) before the argument values are inserted in place of the placeholders.

The format string types that allow embedded named references are:

- Shell format strings.
- In Python, those Python format strings that take a dictionary as argument, and the Python brace format strings.
- In Ruby, those Ruby format strings that take a hash table as argument.
- In Perl, the Perl brace format strings.

### The `<inttypes.h>` macros

A similar case is compile time concatenation of strings. The ISO C 99 include file `<inttypes.h>` contains a macro `PRId64` that can be used as a formatting directive for outputting an ‘`int64_t`’ integer through `printf`. It expands to a constant string, usually "d" or "ld" or "lld" or something like this, depending on the platform. Assume you have code like

    printf ("The amount is %0" PRId64 "\n", number);

The `gettext` tools and library have special support for these `<inttypes.h>` macros. You can therefore simply write

    printf (gettext ("The amount is %0" PRId64 "\n"), number);

The PO file will contain the string "The amount is %0<PRId64>\n". The translators will provide a translation containing "%0<PRId64>" as well, and at runtime the `gettext` function's result will contain the appropriate constant string, "d" or "ld" or "lld".

This works only for the predefined `<inttypes.h>` macros. If you have defined your own similar macros, let's say ‘`MYPRId64`’, that are not known to `xgettext`, the solution for this problem is to change the code like this:

    char buf1[100];
    sprintf (buf1, "%0" MYPRId64, number);
    printf (gettext ("The amount is %s\n"), buf1);

This means, you put the platform dependent code in one statement, and the internationalization code in a different statement. Note that a buffer length of 100 is safe, because all available hardware integer types are limited to 128 bits, and to print a 128 bit integer one needs at most 54 characters, regardless whether in decimal, octal or hexadecimal.

### 4.3.5 No embedded URLs

It is good to not embed URLs in translatable strings, for several reasons:

- It avoids possible mistakes during copy and paste.
- Translators cannot translate the URLs or, by mistake, use the URLs from other packages that are present in their compendium.
- When the URLs change, translators don't need to revisit the translation of the string.

The same holds for email addresses.

So, you would change

    fputs (_("GNU GPL version 3 <https://gnu.org/licenses/gpl.html>\n"),
           stream);

to

    fprintf (stream, _("GNU GPL version 3 <%s>\n"),
             "https://gnu.org/licenses/gpl.html");

### 4.3.6 No programmer-defined format string directives

The GNU C Library's `<printf.h>` facility and the C++ standard library's `<format>` header file make it possible for the programmer to define their own format string directives. However, such format directives cannot be used in translatable strings, for two reasons:

- There is no reference documentation for format strings with such directives, that the translators could consult. They would therefore have to guess where the directive starts and where it ends.
- An ‘`msgfmt -c`’ invocation cannot check whether the translator has produced a compatible translation of the format string. As a consequence, when a format string contains a programmer-defined directive, the program may crash at runtime when it uses the translated format string.

To avoid this situation, you need to move the formatting with the custom directive into a format string that does not get translated.

For example, assuming code that makes use of a `%r` directive:

    fprintf (stream, _("The contents is: %r"), data);

you would rewrite it to:

    char *tmp;
    if (asprintf (&tmp, "%r", data) < 0)
      error (...);
    fprintf (stream, _("The contents is: %s"), tmp);
    free (tmp);

Similarly, in C++, assuming you have defined a custom `formatter` for the type of `data`, the code

    cout << format (_("The contents is: {:#$#}"), data);

should be rewritten to:

    string tmp = format ("{:#$#}", data);
    cout << format (_("The contents is: {}"), tmp);

### 4.3.7 No unusual markup

Unusual markup or control characters should not be used in translatable strings. Translators will likely not understand the particular meaning of the markup or control characters.

For example, if you have a convention that ‘`|`’ delimits the left-hand and right-hand part of some GUI elements, translators will often not understand it without specific comments. It might be better to have the translator translate the left-hand and right-hand part separately.

Another example is the ‘`argp`’ convention to use a single ‘`\v`’ (vertical tab) control character to delimit two sections inside a string. This is flawed. Some translators may convert it to a simple newline, some to blank lines. With some PO file editors it may not be easy to even enter a vertical tab control character. So, you cannot be sure that the translation will contain a ‘`\v`’ character, at the corresponding position. The solution is, again, to let the translator translate two separate strings and combine at run-time the two translated strings with the ‘`\v`’ required by the convention.

HTML markup, however, is common enough that it's probably ok to use in translatable strings. But please bear in mind that the GNU gettext tools don't verify that the translations are well-formed HTML.

## 4.4 How Marks Appear in Sources

All strings requiring translation should be marked in the C sources. Marking is done in such a way that each translatable string appears to be the sole argument of some function or preprocessor macro. There are only a few such possible functions or macros meant for translation, and their names are said to be marking keywords. The marking is attached to strings themselves, rather than to what we do with them. This approach has more uses. A blatant example is an error message produced by formatting. The format string needs translation, as well as some strings inserted through some ‘`%s`’ specification in the format, while the result from `sprintf` may have so many different instances that it is impractical to list them all in some ‘`error_string_out()`’ routine, say.

This marking operation has two goals. The first goal of marking is for triggering the retrieval of the translation, at run time. The keyword is possibly resolved into a routine able to dynamically return the proper translation, as far as possible or wanted, for the argument string. Most localizable strings are found in executable positions, that is, attached to variables or given as parameters to functions. But this is not universal usage, and some translatable strings appear in structured initializations. See section Special Cases of Translatable Strings.

The second goal of the marking operation is to help `xgettext` at properly extracting all translatable strings when it scans a set of program sources and produces PO file templates.

The canonical keyword for marking translatable strings is ‘`gettext`’, it gave its name to the whole GNU `gettext` package. For packages making only light use of the ‘`gettext`’ keyword, macro or function, it is easily used as is. However, for packages using the `gettext` interface more heavily, it is usually more convenient to give the main keyword a shorter, less obtrusive name. Indeed, the keyword might appear on a lot of strings all over the package, and programmers usually do not want nor need their program sources to remind them forcefully, all the time, that they are internationalized. Further, a long keyword has the disadvantage of using more horizontal space, forcing more indentation work on sources for those trying to keep them within 79 or 80 columns.

Many packages use ‘`_`’ (a simple underline) as a keyword, and write ‘`_("Translatable string")`’ instead of ‘`gettext ("Translatable string")`’. Further, the coding rule, from GNU standards, wanting that there is a space between the keyword and the opening parenthesis is relaxed, in practice, for this particular usage. So, the textual overhead per translatable string is reduced to only three characters: the underline and the two parentheses. However, even if GNU `gettext` uses this convention internally, it does not offer it officially. The real, genuine keyword is truly ‘`gettext`’ indeed. It is fairly easy for those wanting to use ‘`_`’ instead of ‘`gettext`’ to declare:

    #include <libintl.h>
    #define _(String) gettext (String)

instead of merely using ‘`#include <libintl.h>`’.

The marking keywords ‘`gettext`’ and ‘`_`’ take the translatable string as sole argument. It is also possible to define marking functions that take it at another argument position. It is even possible to make the marked argument position depend on the total number of arguments of the function call; this is useful in C++. All this is achieved using `xgettext`'s ‘`--keyword`’ option. How to pass such an option to `xgettext`, assuming that `gettextize` is used, is described in ‘`Makevars`’ in ‘`po/`’ and AM_XGETTEXT_OPTION in ‘`po.m4`’.

Note also that long strings can be split across lines, into multiple adjacent string tokens. Automatic string concatenation is performed at compile time according to ISO C and ISO C++; `xgettext` also supports this syntax.

In C++, marking a C++ format string requires a small code change, because the first argument to `std::format` must be a constant expression. For example,

    std::format ("{} {}!", "Hello", "world")

needs to be changed to

    std::vformat (gettext ("{} {}!"), std::make_format_args("Hello", "world"))

Later on, the maintenance is relatively easy. If, as a programmer, you add or modify a string, you will have to ask yourself if the new or altered string requires translation, and include it within ‘`_()`’ if you think it should be translated. For example, ‘`"%s"`’ is an example of string not requiring translation. But ‘`"%s: %d"`’ does require translation, because in French, unlike in English, it's customary to put a space before a colon.

## 4.5 Marking Translatable Strings

In PO mode, one set of features is meant more for the programmer than for the translator, and allows him to interactively mark which strings, in a set of program sources, are translatable, and which are not. Even if it is a fairly easy job for a programmer to find and mark such strings by other means, using any editor of his choice, PO mode makes this work more comfortable. Further, this gives translators who feel a little like programmers, or programmers who feel a little like translators, a tool letting them work at marking translatable strings in the program sources, while simultaneously producing a set of translation in some language, for the package being internationalized.

The set of program sources, targeted by the PO mode commands describe here, should have an Emacs tags table constructed for your project, prior to using these PO file commands. This is easy to do. In any shell window, change the directory to the root of your project, then execute a command resembling:

    etags src/*.[hc] lib/*.[hc]

presuming here you want to process all ‘`.h`’ and ‘`.c`’ files from the ‘`src/`’ and ‘`lib/`’ directories. This command will explore all said files and create a ‘`TAGS`’ file in your root directory, somewhat summarizing the contents using a special file format Emacs can understand.

For packages following the GNU coding standards, there is a make goal `tags` or `TAGS` which constructs the tag files in all directories and for all files containing source code.

Once your ‘`TAGS`’ file is ready, the following commands assist the programmer at marking translatable strings in his set of sources. But these commands are necessarily driven from within a PO file window, and it is likely that you do not even have such a PO file yet. This is not a problem at all, as you may safely open a new, empty PO file, mainly for using these commands. This empty PO file will slowly fill in while you mark strings as translatable in your program sources.

`,`

  Search through program sources for a string which looks like a candidate for translation (`po-tags-search`).

`M-,`

  Mark the last string found with ‘`_()`’ (`po-mark-translatable`).

`M-.`

  Mark the last string found with a keyword taken from a set of possible keywords. This command with a prefix allows some management of these keywords (`po-select-mark-and-mark`).

The `,` (`po-tags-search`) command searches for the next occurrence of a string which looks like a possible candidate for translation, and displays the program source in another Emacs window, positioned in such a way that the string is near the top of this other window. If the string is too big to fit whole in this window, it is positioned so only its end is shown. In any case, the cursor is left in the PO file window. If the shown string would be better presented differently in different native languages, you may mark it using `M-,` or `M-.`. Otherwise, you might rather ignore it and skip to the next string by merely repeating the `,` command.

A string is a good candidate for translation if it contains a sequence of three or more letters. A string containing at most two letters in a row will be considered as a candidate if it has more letters than non-letters. The command disregards strings containing no letters, or isolated letters only. It also disregards strings within comments, or strings already marked with some keyword PO mode knows (see below).

If you have never told Emacs about some ‘`TAGS`’ file to use, the command will request that you specify one from the minibuffer, the first time you use the command. You may later change your ‘`TAGS`’ file by using the regular Emacs command `M-x visit-tags-table`, which will ask you to name the precise ‘`TAGS`’ file you want to use. See (emacs)Tags section `Tag Tables' in The Emacs Editor.

Each time you use the `,` command, the search resumes from where it was left by the previous search, and goes through all program sources, obeying the ‘`TAGS`’ file, until all sources have been processed. However, by giving a prefix argument to the command (`C-u ,`), you may request that the search be restarted all over again from the first program source; but in this case, strings that you recently marked as translatable will be automatically skipped.

Using this `,` command does not prevent using of other regular Emacs tags commands. For example, regular `tags-search` or `tags-query-replace` commands may be used without disrupting the independent `,` search sequence. However, as implemented, the initial `,` command (or the `,` command is used with a prefix) might also reinitialize the regular Emacs tags searching to the first tags file, this reinitialization might be considered spurious.

The `M-,` (`po-mark-translatable`) command will mark the recently found string with the ‘`_`’ keyword. The `M-.` (`po-select-mark-and-mark`) command will request that you type one keyword from the minibuffer and use that keyword for marking the string. Both commands will automatically create a new PO file untranslated entry for the string being marked, and make it the current entry (making it easy for you to immediately proceed to its translation, if you feel like doing it right away). It is possible that the modifications made to the program source by `M-,` or `M-.` render some source line longer than 80 columns, forcing you to break and re-indent this line differently. You may use the `O` command from PO mode, or any other window changing command from Emacs, to break out into the program source window, and do any needed adjustments. You will have to use some regular Emacs command to return the cursor to the PO file window, if you want command `,` for the next string, say.

The `M-.` command has a few built-in speedups, so you do not have to explicitly type all keywords all the time. The first such speedup is that you are presented with a preferred keyword, which you may accept by merely typing `<RET>` at the prompt. The second speedup is that you may type any non-ambiguous prefix of the keyword you really mean, and the command will complete it automatically for you. This also means that PO mode has to know all your possible keywords, and that it will not accept mistyped keywords.

If you reply `?` to the keyword request, the command gives a list of all known keywords, from which you may choose. When the command is prefixed by an argument (`C-u M-.`), it inhibits updating any program source or PO file buffer, and does some simple keyword management instead. In this case, the command asks for a keyword, written in full, which becomes a new allowed keyword for later `M-.` commands. Moreover, this new keyword automatically becomes the preferred keyword for later commands. By typing an already known keyword in response to `C-u M-.`, one merely changes the preferred keyword and does nothing more.

All keywords known for `M-.` are recognized by the `,` command when scanning for strings, and strings already marked by any of those known keywords are automatically skipped. If many PO files are opened simultaneously, each one has its own independent set of known keywords. There is no provision in PO mode, currently, for deleting a known keyword, you have to quit the file (maybe using `q`) and reopen it afresh. When a PO file is newly brought up in an Emacs window, only ‘`gettext`’ and ‘`_`’ are known as keywords, and ‘`gettext`’ is preferred for the `M-.` command. In fact, this is not useful to prefer ‘`_`’, as this one is already built in the `M-,` command.

## 4.6 Adding advice for translators

Sometimes you might want to add advice for the translators to a particular message. For example:

- The translatable string might be decent English but nevertheless ambiguous.
- The translatable string refers to something in English culture (such as a film's name) that is different in other cultures.
- The translator should make an adjustment that is specific to her locale.

The way to do this is to add comments, before the `gettext` invocation or inside the `gettext` invocation but before the string, that start with the substring ‘`TRANSLATORS:`’. These comments will be extracted into the POT file, so that translators can see them. For example, when you write

    /* TRANSLATORS: This is an English idiom,
       meaning not to reveal a secret. */
    puts (gettext ("Don't spill the beans!"));

the POT file will contain:

    #. TRANSLATORS: This is an English idiom,
    #. meaning not to reveal a secret.
    #: source.c:213
    msgid "Don't spill the beans!"
    msgstr ""

and the translators will be shown the advice in a particular place in their translation tool.

Only comments that immediately precede the `gettext` invocation or the translatable string are considered. Intervening blank lines are OK, but if there is other code between the comment and the translatable string, the comment no longer applies.

Note: The string `TRANSLATORS:` is a convention, enabled by the `Makefile.in.in` file that is part of a package's build system. It is not enabled by default in `xgettext`. If you are using `xgettext` without the `Makefile.in.in` infrastructure, you will need to pass the option `--add-comments=TRANSLATORS:` yourself.

## 4.7 Special Comments preceding Keywords

In C programs strings are often used within calls of functions from the `printf` family. The special thing about these format strings is that they can contain format specifiers introduced with `%`. Assume we have the code

    printf (gettext ("String `%s' has %d characters\n"), s, strlen (s));

A possible German translation for the above string might be:

    "%d Zeichen lang ist die Zeichenkette `%s'"

A C programmer, even if he cannot speak German, will recognize that there is something wrong here. The order of the two format specifiers is changed but of course the arguments in the `printf` don't have. This will most probably lead to problems because now the length of the string is regarded as the address.

To prevent errors at runtime caused by translations, the `msgfmt` tool can check statically whether the arguments in the original and the translation string match in type and number. If this is not the case and the ‘`-c`’ option has been passed to `msgfmt`, `msgfmt` will give an error and refuse to produce a MO file. Thus consistent use of ‘`msgfmt -c`’ will catch the error, so that it cannot cause problems at runtime.

If the word order in the above German translation would be correct one would have to write

    "%2$d Zeichen lang ist die Zeichenkette `%1$s'"

The routines in `msgfmt` know about this special notation.

Because not all strings in a program will be format strings, it is not useful for `msgfmt` to test all the strings in the ‘`.po`’ file. This might cause problems because the string might contain what looks like a format specifier, but the string is not used in `printf`.

Therefore `xgettext` adds a special tag to those messages it thinks might be a format string. There is no absolute rule for this, only a heuristic. In the ‘`.po`’ file the entry is marked using the `c-format` flag in the `#,` comment line (see section The Format of PO Files).

The careful reader now might say that this again can cause problems. The heuristic might guess it wrong. This is true and therefore `xgettext` knows about a special kind of comment which lets the programmer take over the decision. If in the same line as or the immediately preceding line to the `gettext` keyword the `xgettext` program finds a comment containing the words `xgettext:c-format`, it will mark the string in any case with the `c-format` flag. This kind of comment should be used when `xgettext` does not recognize the string as a format string but it really is one and it should be tested. Please note that when the comment is in the same line as the `gettext` keyword, it must be before the string to be translated. Also note that a comment such as `xgettext:c-format` applies only to the first string in the same or the next line, not to multiple strings.

This situation happens quite often. The `printf` function is often called with strings which do not contain a format specifier. Of course one would normally use `fputs` but it does happen. In this case `xgettext` does not recognize this as a format string but what happens if the translation introduces a valid format specifier? The `printf` function will try to access one of the parameters but none exists because the original code does not pass any parameters.

`xgettext` of course could make a wrong decision the other way round, i.e. a string marked as a format string actually is not a format string. In this case the `msgfmt` might give too many warnings and would prevent translating the ‘`.po`’ file. The method to prevent this wrong decision is similar to the one used above, only the comment to use must contain the string `xgettext:no-c-format`.

If a string is marked with `c-format` and this is not correct the user can find out who is responsible for the decision. See Invoking the `xgettext` Program to see how the `--debug` option can be used for solving this problem.

## 4.8 Special Cases of Translatable Strings

The attentive reader might now point out that it is not always possible to mark translatable string with `gettext` or something like this. Consider the following case:

    {
      static const char *messages[] = {
        "some very meaningful message",
        "and another one"
      };
      const char *string;
      …
      string
        = index > 1 ? "a default message" : messages[index];

      fputs (string);
      …
    }

While it is no problem to mark the string `"a default message"` it is not possible to mark the string initializers for `messages`. What is to be done? We have to fulfill two tasks. First we have to mark the strings so that the `xgettext` program (see section Invoking the `xgettext` Program) can find them, and second we have to translate the string at runtime before printing them.

The first task can be fulfilled by creating a new keyword, which names a no-op. For the second we have to mark all access points to a string from the array. So one solution can look like this:

    #define gettext_noop(String) String

    {
      static const char *messages[] = {
        gettext_noop ("some very meaningful message"),
        gettext_noop ("and another one")
      };
      const char *string;
      …
      string
        = index > 1 ? gettext ("a default message") : gettext (messages[index]);

      fputs (string);
      …
    }

Please convince yourself that the string which is written by `fputs` is translated in any case. How to get `xgettext` know the additional keyword `gettext_noop` is explained in Invoking the `xgettext` Program.

The above is of course not the only solution. You could also come along with the following one:

    #define gettext_noop(String) String

    {
      static const char *messages[] = {
        gettext_noop ("some very meaningful message"),
        gettext_noop ("and another one")
      };
      const char *string;
      …
      string
        = index > 1 ? gettext_noop ("a default message") : messages[index];

      fputs (gettext (string));
      …
    }

But this has a drawback. The programmer has to take care that he uses `gettext_noop` for the string `"a default message"`. A use of `gettext` could have in rare cases unpredictable results.

One advantage is that you need not make control flow analysis to make sure the output is really translated in any case. But this analysis is generally not very difficult. If it should be in any situation you can use this second method in this situation.

## 4.9 Letting Users Report Translation Bugs

Code sometimes has bugs, but translations sometimes have bugs too. The users need to be able to report them. Reporting translation bugs to the programmer or maintainer of a package is not very useful, since the maintainer must never change a translation, except on behalf of the translator. Hence the translation bugs must be reported to the translators.

Here is a way to organize this so that the maintainer does not need to forward translation bug reports, nor even keep a list of the addresses of the translators or their translation teams.

Every program has a place where is shows the bug report address. For GNU programs, it is the code which handles the “–help” option, typically in a function called “usage”. In this place, instruct the translator to add her own bug reporting address. For example, if that code has a statement

    printf (_("Report bugs to <%s>.\n"), PACKAGE_BUGREPORT);

you can add some translator instructions like this:

    /* TRANSLATORS: The placeholder indicates the bug-reporting address
       for this package.  Please add _another line_ saying
       "Report translation bugs to <...>\n" with the address for translation
       bugs (typically your translation team's web or email address).  */
    printf (_("Report bugs to <%s>.\n"), PACKAGE_BUGREPORT);

These will be extracted by ‘`xgettext`’, leading to a .pot file that contains this:

    #. TRANSLATORS: The placeholder indicates the bug-reporting address
    #. for this package.  Please add _another line_ saying
    #. "Report translation bugs to <...>\n" with the address for translation
    #. bugs (typically your translation team's web or email address).
    #: src/hello.c:178
    #, c-format
    msgid "Report bugs to <%s>.\n"
    msgstr ""

## 4.10 Marking Proper Names for Translation

Should names of persons, cities, locations etc. be marked for translation or not? People who only know languages that can be written with Latin letters (English, Spanish, French, German, etc.) are tempted to say “no”, because names usually do not change when transported between these languages. However, in general when translating from one script to another, names are translated too, usually phonetically or by transliteration. For example, Russian or Greek names are converted to the Latin alphabet when being translated to English, and English or French names are converted to the Katakana script when being translated to Japanese. This is necessary because the speakers of the target language in general cannot read the script the name is originally written in.

As a programmer, you should therefore make sure that names are marked for translation, with a special comment telling the translators that it is a proper name and how to pronounce it. In its simple form, it looks like this:

    printf (_("Written by %s.\n"),
            /* TRANSLATORS: This is a proper name.  See the gettext
               manual, section Names.  Note this is actually a non-ASCII
               name: The first name is (with Unicode escapes)
               "Fran\u00e7ois" or (with HTML entities) "Fran&ccedil;ois".
               Pronunciation is like "fraa-swa pee-nar".  */
            _("Francois Pinard"));

The GNU gnulib library offers a module ‘`propername`’ (https://www.gnu.org/software/gnulib/MODULES.html#module=propername) which takes care to automatically append the original name, in parentheses, to the translated name. For names that cannot be written in ASCII, it also frees the translator from the task of entering the appropriate non-ASCII characters if no script change is needed. In this more comfortable form, it looks like this:

    printf (_("Written by %s and %s.\n"),
            proper_name ("Ulrich Drepper"),
            /* TRANSLATORS: This is a proper name.  See the gettext
               manual, section Names.  Note this is actually a non-ASCII
               name: The first name is (with Unicode escapes)
               "Fran\u00e7ois" or (with HTML entities) "Fran&ccedil;ois".
               Pronunciation is like "fraa-swa pee-nar".  */
            proper_name_utf8 ("Francois Pinard", "Fran\303\247ois Pinard"));

You can also write the original name directly in Unicode (rather than with Unicode escapes or HTML entities) and denote the pronunciation using the International Phonetic Alphabet (see https://en.wikipedia.org/wiki/International_Phonetic_Alphabet).

As a translator, you should use some care when translating names, because it is frustrating if people see their names mutilated or distorted.

If your language uses the Latin script, all you need to do is to reproduce the name as perfectly as you can within the usual character set of your language. In this particular case, this means to provide a translation containing the c-cedilla character. If your language uses a different script and the people speaking it don't usually read Latin words, it means transliteration. If the programmer used the simple case, you should still give, in parentheses, the original writing of the name – for the sake of the people that do read the Latin script. If the programmer used the ‘`propername`’ module mentioned above, you don't need to give the original writing of the name in parentheses, because the program will already do so. Here is an example, using Greek as the target script:

    #. This is a proper name.  See the gettext
    #. manual, section Names.  Note this is actually a non-ASCII
    #. name: The first name is (with Unicode escapes)
    #. "Fran\u00e7ois" or (with HTML entities) "Fran&ccedil;ois".
    #. Pronunciation is like "fraa-swa pee-nar".
    msgid "Francois Pinard"
    msgstr "\phi\rho\alpha\sigma\omicron\alpha \pi\iota\nu\alpha\rho"
           " (Francois Pinard)"

Because translation of names is such a sensitive domain, it is a good idea to test your translation before submitting it.

## 4.11 Preparing Library Sources

When you are preparing a library, not a program, for the use of `gettext`, only a few details are different. Here we assume that the library has a translation domain and a POT file of its own. (If it uses the translation domain and POT file of the main program, then the previous sections apply without changes.)

1. The library code doesn't call `setlocale (LC_ALL, "")`. It's the responsibility of the main program to set the locale. The library's documentation should mention this fact, so that developers of programs using the library are aware of it.
2. The library code doesn't call `textdomain (PACKAGE)`, because it would interfere with the text domain set by the main program.
3. The initialization code for a program was

         setlocale (LC_ALL, "");
         bindtextdomain (PACKAGE, LOCALEDIR);
         textdomain (PACKAGE);

   For a library it is reduced to

         bindtextdomain (PACKAGE, LOCALEDIR);

   If your library's API doesn't already have an initialization function, you need to create one, containing at least the `bindtextdomain` invocation. However, you usually don't need to export and document this initialization function: It is sufficient that all entry points of the library call the initialization function if it hasn't been called before. The typical idiom used to achieve this is a static boolean variable that indicates whether the initialization function has been called. If the library is meant to be used in multithreaded applications, this variable needs to be marked `volatile`, so that its value get propagated between threads. Like this:

       static volatile bool libfoo_initialized;

       static void
       libfoo_initialize (void)
       {
         bindtextdomain (PACKAGE, LOCALEDIR);
         libfoo_initialized = true;
       }

       /* This function is part of the exported API.  */
       struct foo *
       create_foo (...)
       {
         /* Must ensure the initialization is performed.  */
         if (!libfoo_initialized)
           libfoo_initialize ();
         ...
       }

       /* This function is part of the exported API.  The argument must be
          non-NULL and have been created through create_foo().  */
       int
       foo_refcount (struct foo *argument)
       {
         /* No need to invoke the initialization function here, because
            create_foo() must already have been called before.  */
         ...
       }

   The more general solution for initialization functions, POSIX `pthread_once`, is not needed in this case.

4. The usual declaration of the ‘`_`’ macro in each source file was

       #include <libintl.h>
       #define _(String) gettext (String)

   for a program. For a library, which has its own translation domain, it reads like this:

       #include <libintl.h>
       #define _(String) dgettext (PACKAGE, String)

   In other words, `dgettext` is used instead of `gettext`. Similarly, the `dngettext` function should be used in place of the `ngettext` function.

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