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GNU gettext utilities: 3. The Format of PO Files

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3. The Format of PO Files

The GNU gettext toolset helps programmers and translators at producing, updating and using translation files, mainly those PO files which are textual, editable files. This chapter explains the format of PO files.

A PO file is made up of many entries, each entry holding the relation between an original untranslated string and its corresponding translation. All entries in a given PO file usually pertain to a single project, and all translations are expressed in a single target language. One PO file entry has the following schematic structure:

white-space
#  translator-comments
#. extracted-comments
#: reference…
#, flag…
#| msgid previous-untranslated-string
msgid untranslated-string
msgstr translated-string

The general structure of a PO file should be well understood by the translator. When using PO mode, very little has to be known about the format details, as PO mode takes care of them for her.

A simple entry can look like this:

#: lib/error.c:116
msgid "Unknown system error"
msgstr "Error desconegut del sistema"

Entries begin with some optional white space. Usually, when generated through GNU gettext tools, there is exactly one blank line between entries. Then comments follow, on lines all starting with the character #. There are two kinds of comments: those which have some white space immediately following the # - the translator comments -, which comments are created and maintained exclusively by the translator, and those which have some non-white character just after the # - the automatic comments -, which comments are created and maintained automatically by GNU gettext tools. Comment lines starting with #. contain comments given by the programmer, directed at the translator; these comments are called extracted comments because the xgettext program extracts them from the program's source code. Comment lines starting with #: contain references to the program's source code. Comment lines starting with #, contain flags; more about these below. Comment lines starting with #| contain the previous untranslated string for which the translator gave a translation.

All comments, of either kind, are optional.

After white space and comments, entries show two strings, namely first the untranslated string as it appears in the original program sources, and then, the translation of this string. The original string is introduced by the keyword msgid, and the translation, by msgstr. The two strings, untranslated and translated, are quoted in various ways in the PO file, using " delimiters and \ escapes, but the translator does not really have to pay attention to the precise quoting format, as PO mode fully takes care of quoting for her.

The msgid strings, as well as automatic comments, are produced and managed by other GNU gettext tools, and PO mode does not provide means for the translator to alter these. The most she can do is merely deleting them, and only by deleting the whole entry. On the other hand, the msgstr string, as well as translator comments, are really meant for the translator, and PO mode gives her the full control she needs.

The comment lines beginning with #, are special because they are not completely ignored by the programs as comments generally are. The comma separated list of flags is used by the msgfmt program to give the user some better diagnostic messages. Currently there are two forms of flags defined:

fuzzy

This flag can be generated by the msgmerge program or it can be inserted by the translator herself. It shows that the msgstr string might not be a correct translation (anymore). Only the translator can judge if the translation requires further modification, or is acceptable as is. Once satisfied with the translation, she then removes this fuzzy attribute. The msgmerge program inserts this when it combined the msgid and msgstr entries after fuzzy search only. See section Fuzzy Entries.

c-format

no-c-format

These flags should not be added by a human. Instead only the xgettext program adds them. In an automated PO file processing system as proposed here, the user's changes would be thrown away again as soon as the xgettext program generates a new template file.

The c-format flag indicates that the untranslated string and the translation are supposed to be C format strings. The no-c-format flag indicates that they are not C format strings, even though the untranslated string happens to look like a C format string (with ‘%’ directives).

When the c-format flag is given for a string the msgfmt program does some more tests to check the validity of the translation. See section Invoking the msgfmt Program, Special Comments preceding Keywords and C Format Strings.

objc-format

no-objc-format

Likewise for Objective C, see Objective C Format Strings.

python-format

no-python-format

Likewise for Python, see Python Format Strings.

python-brace-format

no-python-brace-format

Likewise for Python brace, see Python Format Strings.

java-format

no-java-format

Likewise for Java MessageFormat format strings, see Java Format Strings.

java-printf-format

no-java-printf-format

Likewise for Java printf format strings, see Java Format Strings.

csharp-format

no-csharp-format

Likewise for C#, see C# Format Strings.

javascript-format

no-javascript-format

Likewise for JavaScript, see JavaScript Format Strings.

scheme-format

no-scheme-format

Likewise for Scheme, see Scheme Format Strings.

lisp-format

no-lisp-format

Likewise for Lisp, see Lisp Format Strings.

elisp-format

no-elisp-format

Likewise for Emacs Lisp, see Emacs Lisp Format Strings.

librep-format

no-librep-format

Likewise for librep, see librep Format Strings.

ruby-format

no-ruby-format

Likewise for Ruby, see Ruby Format Strings.

sh-format

no-sh-format

Likewise for Shell, see Shell Format Strings.

awk-format

no-awk-format

Likewise for awk, see awk Format Strings.

lua-format

no-lua-format

Likewise for Lua, see Lua Format Strings.

object-pascal-format

no-object-pascal-format

Likewise for Object Pascal, see Object Pascal Format Strings.

smalltalk-format

no-smalltalk-format

Likewise for Smalltalk, see Smalltalk Format Strings.

qt-format

no-qt-format

Likewise for Qt, see Qt Format Strings.

qt-plural-format

no-qt-plural-format

Likewise for Qt plural forms, see Qt Format Strings.

kde-format

no-kde-format

Likewise for KDE, see KDE Format Strings.

boost-format

no-boost-format

Likewise for Boost, see Boost Format Strings.

tcl-format

no-tcl-format

Likewise for Tcl, see Tcl Format Strings.

perl-format

no-perl-format

Likewise for Perl, see Perl Format Strings.

perl-brace-format

no-perl-brace-format

Likewise for Perl brace, see Perl Format Strings.

php-format

no-php-format

Likewise for PHP, see PHP Format Strings.

gcc-internal-format

no-gcc-internal-format

Likewise for the GCC sources, see GCC internal Format Strings.

gfc-internal-format

no-gfc-internal-format

Likewise for the GNU Fortran Compiler sources, see GFC internal Format Strings.

ycp-format

no-ycp-format

Likewise for YCP, see YCP Format Strings.

It is also possible to have entries with a context specifier. They look like this:

white-space
#  translator-comments
#. extracted-comments
#: reference…
#, flag…
#| msgctxt previous-context
#| msgid previous-untranslated-string
msgctxt context
msgid untranslated-string
msgstr translated-string

The context serves to disambiguate messages with the same untranslated-string. It is possible to have several entries with the same untranslated-string in a PO file, provided that they each have a different context. Note that an empty context string and an absent msgctxt line do not mean the same thing.

A different kind of entries is used for translations which involve plural forms.

white-space
#  translator-comments
#. extracted-comments
#: reference…
#, flag…
#| msgid previous-untranslated-string-singular
#| msgid_plural previous-untranslated-string-plural
msgid untranslated-string-singular
msgid_plural untranslated-string-plural
msgstr[0] translated-string-case-0
...
msgstr[N] translated-string-case-n

Such an entry can look like this:

#: src/msgcmp.c:338 src/po-lex.c:699
#, c-format
msgid "found %d fatal error"
msgid_plural "found %d fatal errors"
msgstr[0] "s'ha trobat %d error fatal"
msgstr[1] "s'han trobat %d errors fatals"

Here also, a msgctxt context can be specified before msgid, like above.

Here, additional kinds of flags can be used:

range:: This flag is followed by a range of non-negative numbers, using the syntax range: minimum-value..maximum-value. It designates the possible values that the numeric parameter of the message can take. In some languages, translators may produce slightly better translations if they know that the value can only take on values between 0 and 10, for example.

The previous-untranslated-string is optionally inserted by the msgmerge program, at the same time when it marks a message fuzzy. It helps the translator to see which changes were done by the developers on the untranslated-string.

It happens that some lines, usually whitespace or comments, follow the very last entry of a PO file. Such lines are not part of any entry, and will be dropped when the PO file is processed by the tools, or may disturb some PO file editors.

The remainder of this section may be safely skipped by those using a PO file editor, yet it may be interesting for everybody to have a better idea of the precise format of a PO file. On the other hand, those wishing to modify PO files by hand should carefully continue reading on.

An empty untranslated-string is reserved to contain the header entry with the meta information (see section Filling in the Header Entry). This header entry should be the first entry of the file. The empty untranslated-string is reserved for this purpose and must not be used anywhere else.

Each of untranslated-string and translated-string respects the C syntax for a character string, including the surrounding quotes and embedded backslashed escape sequences. When the time comes to write multi-line strings, one should not use escaped newlines. Instead, a closing quote should follow the last character on the line to be continued, and an opening quote should resume the string at the beginning of the following PO file line. For example:

msgid ""
"Here is an example of how one might continue a very long string\n"
"for the common case the string represents multi-line output.\n"

In this example, the empty string is used on the first line, to allow better alignment of the H from the word ‘Here’ over the f from the word ‘for’. In this example, the msgid keyword is followed by three strings, which are meant to be concatenated. Concatenating the empty string does not change the resulting overall string, but it is a way for us to comply with the necessity of msgid to be followed by a string on the same line, while keeping the multi-line presentation left-justified, as we find this to be a cleaner disposition. The empty string could have been omitted, but only if the string starting with ‘Here’ was promoted on the first line, right after msgid.(2) It was not really necessary either to switch between the two last quoted strings immediately after the newline ‘\n’, the switch could have occurred after any other character, we just did it this way because it is neater.

One should carefully distinguish between end of lines marked as ‘\n’ inside quotes, which are part of the represented string, and end of lines in the PO file itself, outside string quotes, which have no incidence on the represented string.

Outside strings, white lines and comments may be used freely. Comments start at the beginning of a line with ‘#’ and extend until the end of the PO file line. Comments written by translators should have the initial ‘#’ immediately followed by some white space. If the ‘#’ is not immediately followed by white space, this comment is most likely generated and managed by specialized GNU tools, and might disappear or be replaced unexpectedly when the PO file is given to msgmerge.