PO4A.7(1) User Contributed Perl Documentation PO4A.7(1)

po4a - framework to translate documentation and other materials

po4a (PO for anything) eases the maintenance of documentation translation using the classical gettext tools. The main feature of po4a is that it decouples the translation of content from its document structure.

This document serves as an introduction to the po4a project with a focus on potential users considering whether to use this tool and on the curious wanting to understand why things are the way they are.

The philosophy of Free Software is to make the technology truly available to everyone. But licensing is not the only consideration: untranslated free software is useless for non-English speakers. Therefore, we still have some work to do to make software available to everybody.

This situation is well understood by most projects and everybody is now convinced of the necessity to translate everything. Yet, the actual translations represent a huge effort of many individuals, crippled by small technical difficulties.

Thankfully, Open Source software is actually very well translated using the gettext tool suite. These tools are used to extract the strings to translate from a program and present the strings to translate in a standardized format (called PO files, or translation catalogs). A whole ecosystem of tools has emerged to help the translators actually translate these PO files. The result is then used by gettext at run time to display translated messages to the end users.

Regarding documentation, however, the situation still somewhat disappointing. At first translating documentation may seem to be easier than translating a program as it would seem that you just have to copy the documentation source file and start translating the content. However, when the original documentation is modified, keeping track of the modifications quickly turns into a nightmare for the translators. If done manually, this task is unpleasant and error-prone.

Outdated translations are often worse than no translation at all. End-users can be tricked by documentation describing an old behavior of the program. Furthermore, they cannot interact directly with the maintainers since they don't speak English. Additionally, the maintainer cannot fix the problem as they don't know every language in which their documentation is translated. These difficulties, often caused by poor tooling, can undermine the motivation of volunteer translators, further aggravating the problem.

The goal of the po4a project is to ease the work of documentation translators. In particular, it makes documentation translations maintainable.

The idea is to reuse and adapt the gettext approach to this field. As with gettext, texts are extracted from their original locations and presented to translators as PO translation catalogs. The translators can leverage the classical gettext tools to monitor the work to do, collaborate and organize as teams. po4a then injects the translations directly into the documentation structure to produce translated source files that can be processed and distributed just like the English files. Any paragraph that is not translated is left in English in the resulting document, ensuring that the end users never see an outdated translation in the documentation.

This automates most of the grunt work of the translation maintenance. Discovering the paragraphs needing an update becomes very easy, and the process is completely automated when elements are reordered without further modification. Specific verification can also be used to reduce the chance of formatting errors that would result in a broken document.

Please also see the FAQ below in this document for a more complete list of the advantages and disadvantages of this approach.

Currently, this approach has been successfully implemented to several kinds of text formatting formats:

The good old manual pages' format, used by so many programs out there. po4a support is very welcome here since this format is somewhat difficult to use and not really friendly to newbies.

The Locale::Po4a::Man(3pm) module also supports the mdoc format, used by the BSD man pages (they are also quite common on Linux).

This format is a lightweight markup format intended to ease the authoring of documentation. It is for example used to document the git system. Those manpages are translated using po4a.

See Locale::Po4a::AsciiDoc for details.

This is the Perl Online Documentation format. The language and extensions themselves are documented using this format in addition to most existing Perl scripts. It makes easy to keep the documentation close to the actual code by embedding them both in the same file. It makes programmer's life easier, but unfortunately, not the translator's, until you use po4a.

See Locale::Po4a::Pod for details.

Even if superseded by XML nowadays, this format is still used for documents which are more than a few screens long. It can even be used for complete books. Documents of this length can be very challenging to update. diff often reveals useless when the original text was re-indented after update. Fortunately, po4a can help you after that process.

Currently, only DebianDoc and DocBook DTD are supported, but adding support for a new one is really easy. It is even possible to use po4a on an unknown SGML DTD without changing the code by providing the needed information on the command line. See Locale::Po4a::Sgml(3pm) for details.

The LaTeX format is a major documentation format used in the Free Software world and for publications.

The Locale::Po4a::LaTeX(3pm) module was tested with the Python documentation, a book and some presentations.

The Text format is the base format for many formats that include long blocks of text, including Markdown, fortunes, YAML front matter section, debian/changelog, and debian/control.

This supports the common format used in Static Site Generators, READMEs, and other documentation systems. See Locale::Po4a::Text(3pm) for details.

The XML format is a base format for many documentation formats.

Currently, the DocBook DTD (see Locale::Po4a::Docbook(3pm) for details) and XHTML are supported by po4a.

The BibTex format is used alongside LaTex for formatting lists of references (bibliographies).

See Locale::Po4a::BibTex for details.

A XML-based markup language that uses semantic tags to describe documents.

See Locale::Po4a:Docbook for greater details.

A XML documentation format. This module was developed specifically to help with supporting and maintaining translations of Gentoo Linux documentation up until at least March 2016 (Based on the Wayback Machine). Gentoo have since moved to the DevBook XML format.

See Locale::Po4a:Guide for greater details.

The Web Markup Language, do not mixup WML with the WAP stuff used on cell phones. This module relies on the Xhtml module, which itself relies on the XmL module.

See Locale::Po4a::Wml for greater details.

A strict superset of JSON. YAML is often used as systems or configuration projects. YAML is at the core of Red Hat's Ansible.

See Locale::Po4a::Yaml for greater details.

The Ruby Document (RD) format, originally the default documentation format for Ruby and Ruby projects before converted to RDoc in 2002. Though apparently the Japanese version of the Ruby Reference Manual still use RD.

See Locale::Po4a::RubyDoc for greater details.

A documentation production system, with elements similar to TeX, debiandoc-sgml, TeXinfo, and others, developed by Simon Tatham, the developer of PuTTY.

See Locale::Po4a:Halibut for greater details.

Configuration file format popularized by MS-DOS.

See Locale::Po4a::Ini for greater details.

All of the GNU documentation is written in this format (it's even one of the requirements to become an official GNU project). The support for Locale::Po4a::Texinfo(3pm) in po4a is still at the beginning. Please report bugs and feature requests.
The native plain text format of the Gemini protocol. The extension ".gmi" is commonly used. Support for this module in po4a is still in its infancy. If you find anything, please file a bug or feature request.
Po4a can also handle some more rare or specialized formats, such as the documentation of compilation options for the 2.4+ Linux kernels (Locale::Po4a::KernelHelp) or the diagrams produced by the dia tool (Locale::Po4a:Dia). Adding a new format is often very easy and the main task is to come up with a parser for your target format. See Locale::Po4a::TransTractor(3pm) for more information about this.
Unfortunately, po4a still lacks support for several documentation formats. Many of them would be easy to support in po4a. This includes formats not just used for documentation, such as, package descriptions (deb and rpm), package installation scripts questions, package changelogs, and all the specialized file formats used by programs such as game scenarios or wine resource files.

The easiest way to use this tool in your project is to write a configuration file for the po4a program, and only interact with this program. Please refer to its documentation, in po4a(1). The rest of this section provides more details for the advanced users of po4a wanting to deepen their understanding.

Make sure to read po4a(1) before this overly detailed section to get a simplified overview of the po4a workflow. Come back here when you want to get the full scary picture, with almost all details.

In the following schema, master.doc is an example name for the documentation to be translated; XX.doc is the same document translated in the language XX while doc.XX.po is the translation catalog for that document in the XX language. Documentation authors will mostly be concerned with master.doc (which can be a manpage, an XML document, an AsciidDoc file, etc); the translators will be mostly concerned with the PO file, while the end users will only see the XX.doc file.

Transitions with square brackets such as "[po4a updates po]" represent the execution of a po4a tool while transitions with curly brackets such as "{update of master.doc}" represent a manual modification of the project's files.

                                   master.doc
                                       |
                                       V
     +<-----<----+<-----<-----<--------+------->-------->-------+
     :           |                     |                        :
{translation}    |          {update of master.doc}              :
     :           |                     |                        :
   XX.doc        |                     V                        V
 (optional)      |                 master.doc ->-------->------>+
     :           |                   (new)                      |
     V           V                     |                        |
  [po4a-gettextize]   doc.XX.po -->+   |                        |
          |            (old)       |   |                        |
          |              ^         V   V                        |
          |              |   [po4a updates po]                  |
          V              |           |                          V
   translation.pot       ^           V                          |
          |              |        doc.XX.po                     |
          |              |         (fuzzy)                      |
    {translation}        |           |                          |
          |              ^           V                          V
          |              |     {manual editing}                 |
          |              |           |                          |
          V              |           V                          V
      doc.XX.po --->---->+<---<-- doc.XX.po    addendum     master.doc
      (initial)                 (up-to-date)  (optional)   (up-to-date)
          :                          |            |             |
          :                          V            |             |
          +----->----->----->------> +            |             |
                                     |            |             |
                                     V            V             V
                                     +------>-----+------<------+
                                                  |
                                                  V
                                     [po4a updates translations]
                                                  |
                                                  V
                                                XX.doc
                                             (up-to-date)

Again, this schema is overly complicated. Check on po4a(1) for a simplified overview.

The left part depicts how po4a-gettextize(1) can be used to convert an existing translation project to the po4a infrastructure. This script takes an original document and its translated counterpart, and tries to build the corresponding PO file. Such manual conversion is rather cumbersome (see the po4a-gettextize(1) documentation for more details), but it is only needed once to convert your existing translations. If you don't have any translation to convert, you can forget about this and focus on the right part of the schema.

On the top right part, the action of the original author is depicted, updating the documentation. The middle right part depicts the automatic updates of translation files: the new material is extracted and compared against the exiting translation. The previous translation is used for the parts that didn't change, while partially modified parts are connected to the previous translation with a "fuzzy" marker indicating that the translation must be updated. New or heavily modified material is left untranslated.

Then, the manual editing block depicts the action of the translators, that modify the PO files to provide translations to every original string and paragraph. This can be done using either a specific editor such as the GNOME Translation Editor, KDE's Lokalize or poedit, or using an online localization platform such as weblate or pootle. The translation result is a set of PO files, one per language. Please refer to the gettext documentation for more details.

The bottom part of the figure shows how po4a creates a translated source document from the master.doc original document and the doc.XX.po translation catalog that was updated by the translators. The structure of the document is reused, while the original content is replaced by its translated counterpart. Optionally, an addendum can be used to add some extra text to the translation. This is often used to add the name of the translator to the final document. See below for details.

Upon invocation, po4a updates both the translation files and the translated documentation files automatically.

If you start from scratch, you just have to write a configuration file for po4a, and you are set. The relevant templates are created for the missing files, allowing your contributors to translate your project to their language. Please refer to po4a(1) for a quick start tutorial and for all details.

If you have an existing translation, i.e. a documentation file that was translated manually, you can integrate its content in your po4a workflow using po4a-gettextize. This task is a bit cumbersome (as described in the tool's manpage), but once your project is converted to po4a workflow, everything will be updated automatically.

Once setup, invoking po4a is enough to update both the translation PO files and translated documents. You may pass the "--no-translations" to po4a to not update the translations (thus only updating the PO files) or "--no-update" to not update the PO files (thus only updating the translations). This roughly corresponds to the individual po4a-updatepo and po4a-translate scripts which are now deprecated (see "Why are the individual scripts deprecated" in the FAQ below).

Adding new text to the translation is probably the only thing that is easier in the long run when you translate files manually :). This happens when you want to add an extra section to the translated document, not corresponding to any content in the original document. The classical use case is to give credits to the translation team, and to indicate how to report translation-specific issues.

With po4a, you have to specify addendum files, that can be conceptually viewed as patches applied to the localized document after processing. Each addendum must be provided as a separate file, which format is however very different from the classical patches. The first line is a header line, defining the insertion point of the addendum (with an unfortunately cryptic syntax -- see below) while the rest of the file is added verbatim at the determined position.

The header line must begin with the string PO4A-HEADER:, followed by a semi-colon separated list of key=value fields.

For example, the following header declares an addendum that must be placed at the very end of the translation.

PO4A-HEADER: mode=eof

Things are more complex when you want to add your extra content in the middle of the document. The following header declares an addendum that must be placed after the XML section containing the string "About this document" in translation.

PO4A-HEADER: position=About this document; mode=after; endboundary=</section>

In practice, when trying to apply an addendum, po4a searches for the first line matching the "position" argument (this can be a regexp). Do not forget that po4a considers the translated document here. This documentation is in English, but your line should probably read as follows if you intend your addendum to apply to the French translation of the document.

PO4A-HEADER: position=À propos de ce document; mode=after; endboundary=</section>

Once the "position" is found in the target document, po4a searches for the next line after the "position" that matches the provided "endboundary". The addendum is added right after that line (because we provided an endboundary, i.e. a boundary ending the current section).

The exact same effect could be obtained with the following header, that is equivalent:

PO4A-HEADER: position=About this document; mode=after; beginboundary=<section>

Here, po4a searches for the first line matching "<section>" after the line matching "About this document" in the translation, and add the addendum before that line since we provided a beginboundary, i.e. a boundary marking the beginning of the next section. So this header line requires placing the addendum after the section containing "About this document", and instruct po4a that a section starts with a line containing the "<section>" tag. This is equivalent to the previous example because what you really want is to add this addendum either after "</section>" or before "<section>".

You can also set the insertion mode to the value "before", with a similar semantic: combining "mode=before" with an "endboundary" will put the addendum just after the matched boundary, that is the last potential boundary line before the "position". Combining "mode=before" with an "beginboundary" will put the addendum just before the matched boundary, that is the last potential boundary line before the "position".

 Mode   | Boundary kind |     Used boundary      | Insertion point compared to the boundary
========|===============|========================|=========================================
'before'| 'endboundary' | last before 'position' | Right after the selected boundary
'before'|'beginboundary'| last before 'position' | Right before the selected boundary
'after' | 'endboundary' | first after 'position' | Right after the selected boundary
'after' |'beginboundary'| first after 'position' | Right before the selected boundary
'eof'   |   (none)      |  n/a                   | End of file

Hint and tricks about addenda

  • Remember that these are regexp. For example, if you want to match the end of a nroff section ending with the line ".fi", do not use ".fi" as endboundary, because it will match with "the[ fi]le", which is obviously not what you expect. The correct endboundary in that case is: "^\.fi$".
  • White spaces ARE important in the content of the "position" and boundaries. So the two following lines are different. The second one will only be found if there is enough trailing spaces in the translated document.
    PO4A-HEADER: position=About this document; mode=after; beginboundary=<section>
    PO4A-HEADER: position=About this document ; mode=after; beginboundary=<section>
    
  • Although this context search may be considered to operate roughly on each line of the translated document, it actually operates on the internal data string of the translated document. This internal data string may be a text spanning a paragraph containing multiple lines or may be a XML tag itself alone. The exact insertion point of the addendum must be before or after the internal data string and can not be within the internal data string.
  • Pass the "-vv" argument to po4a to understand how the addenda are added to the translation. It may also help to run po4a in debug mode to see the actual internal data string when your addendum does not apply.

Addenda examples

  • If you want to add something after the following nroff section:
    .SH "AUTHORS"
    

    You should select a two-step approach by setting mode=after. Then you should narrow down search to the line after AUTHORS with the position argument regex. Then, you should match the beginning of the next section (i.e., ^\.SH) with the beginboundary argument regex. That is to say:

    PO4A-HEADER:mode=after;position=AUTHORS;beginboundary=\.SH
    
  • If you want to add something right after a given line (e.g. after the line "Copyright Big Dude"), use a position matching this line, mode=after and give a beginboundary matching any line.
    PO4A-HEADER:mode=after;position=Copyright Big Dude, 2004;beginboundary=^
    
  • If you want to add something at the end of the document, give a position matching any line of your document (but only one line. Po4a won't proceed if it's not unique), and give an endboundary matching nothing. Don't use simple strings here like "EOF", but prefer those which have less chance to be in your document.
    PO4A-HEADER:mode=after;position=About this document;beginboundary=FakePo4aBoundary
    

More detailed example

Original document (POD formatted):

|=head1 NAME
|
|dummy - a dummy program
|
|=head1 AUTHOR
|
|me

Then, the following addendum will ensure that a section (in French) about the translator is added at the end of the file (in French, "TRADUCTEUR" means "TRANSLATOR", and "moi" means "me").

|PO4A-HEADER:mode=after;position=AUTEUR;beginboundary=^=head
|
|=head1 TRADUCTEUR
|
|moi
|

To put your addendum before the AUTHOR, use the following header:

PO4A-HEADER:mode=after;position=NOM;beginboundary=^=head1

This works because the next line matching the beginboundary "/^=head1/" after the section "NAME" (translated to "NOM" in French), is the one declaring the authors. So, the addendum will be put between both sections. Note that if another section is added between NAME and AUTHOR sections later, po4a will wrongfully put the addenda before the new section.

To avoid this you may accomplish the same using mode=before:

PO4A-HEADER:mode=before;position=^=head1 AUTEUR

This chapter gives you a brief overview of the po4a internals, so that you may feel more confident to help us to maintain and to improve it. It may also help you to understand why it does not do what you expected, and how to solve your problems.

At the core of the po4a project, the Locale::Po4a::TransTractor(3pm) class is the common ancestor to all po4a parsers. This strange name comes from the fact that it is at the same time in charge of translating document and extracting strings.

More formally, it takes a document to translate plus a PO file containing the translations to use as input while producing two separate outputs: Another PO file (resulting of the extraction of translatable strings from the input document), and a translated document (with the same structure as the input one, but with all translatable strings replaced with content of the input PO). Here is a graphical representation of this:

Input document --\                             /---> Output document
                  \      TransTractor::       /       (translated)
                   +-->--   parse()  --------+
                  /                           \
Input PO --------/                             \---> Output PO
                                                    (extracted)

This little bone is the core of all the po4a architecture. If you provide both input and disregard the output PO, you get po4a-translate. If you disregard the output document instead, you get po4a-updatepo. The po4a uses a first TransTractor to get an up-to-date output POT file (disregarding the output documents), calls msgmerge -U to update the translation PO files on disk, and builds a second TransTractor with these updated PO files to update the output documents. In short, po4a provides one-stop solution to update what needs to be, using a single configuration file.

po4a-gettextize also uses two TransTractors, but another way: It builds one TransTractor per language, and then build a new PO file using the msgids of the original document as msgids, and the msgids of the translated document as msgstrs. Much care is needed to ensure that the strings matched this way actually match, as described in po4a-gettextize(1).

All po4a format parsers are implemented on top of the TransTractor. Some of them are very simple, such as the Text, Markdown and AsciiDoc ones. They load the lines one by one using TransTractor::shiftline(), accumulate the paragraphs' content or whatever. Once a string is completely parsed, the parser uses TransTractor::translate() to (1) add this string to the output PO file and (2) get the translation from the input PO file. The parser then pushes the result to the output file using TransTractor::pushline().

Some other parsers are more complex because they rely on an external parser to analyze the input document. The Xml, HTML, SGML and Pod parsers are built on top of SAX parsers. They declare callbacks to events such as "I found a new title which content is the following" to update the output document and output POT files according to the input content using TransTractor::translate() and TransTractor::pushline(). The Yaml parser is similar but different: it serializes a data structure produced by the YAML::Tiny parser. This is why the Yaml module of po4a fails to declare the reference lines: the location of each string in the input file is not kept by the parser, so we can only provide "$filename:1" as a string location. The SAX-oriented parsers use globals and other tricks to save the file name and line numbers of references.

One specific issue arises from file encodings and BOM markers. Simple parsers can forget about this issue, that is handled by TransTractor::read() (used internally to get the lines of an input document), but the modules relying on an external parser must ensure that all files are read with an appropriate PerlIO decoding layer. The easiest is to open the file yourself, and provide an filehandle or directly the full string to your external parser. Check on Pod::read() and Pod::parse() for an example. The content read by the TransTractor is ignored, but a fresh filehandle is passed to the external parser. The important part is the "<:encoding($charset)" mode that is passed to the open() perl function.

The Locale::Po4a::Po(3pm) class is in charge of loading and using PO and POT files. Basically, you can read a file, add entries, get translations with the gettext() method, write the PO into a file. More advanced features such as merging a PO file against a POT file or validating a file are delegated to msgmerge and msgfmt respectively.

Even if you have never contributed to any Open Source project in the past, you are welcome: we are willing to help and mentor you here. po4a is best maintained by its users nowadays. As we lack manpower, we try to make the project welcoming by improving the doc and the automatic tests to make you confident in contributing to the project. Please refer to the CONTRIBUTING.md file for more details.

Here is a very partial list of projects that use po4a in production for their documentation. If you want to add your project to the list, just drop us an email (or a Merge Request).

I personally vocalize it as pouah https://en.wiktionary.org/wiki/pouah, which is a French onomatopoetic that we use in place of yuck :) I may have a strange sense of humor :)

Indeed, po4a-updatepo and po4a-translate are deprecated in favor of po4a. The reason is that while po4a can be used as a drop-in replacement to these scripts, there is quite a lot of code duplication here. Individual scripts last around 150 lines of codes while the po4a program lasts 1200 lines, so they do a lot in addition of the common internals. The code duplication results in bugs occuring in both versions and needing two fixes. One example of such duplication are the bugs #1022216 in Debian and the issue #442 in GitHub that had the exact same fix, but one in po4a and the other po4a-updatepo.

In the long run, I would like to drop the individual scripts and only maintain one version of this code. The sure thing is that the individual scripts will not get improved anymore, so only po4a will get the new features. That being said, there is no deprecation urgency. I plan to keep the individual scripts as long as possible, and at least until 2030. If your project still use po4a-updatepo and po4a-translate in 2030, you may have a problem.

We may also remove the deprecation of these scripts at some point, if a refactoring reduces the code duplication to zero. If you have an idea (or better: a patch), your help is welcome.

There are a few of them. Here is a possibly incomplete list, and more tools are coming at the horizon.

This is the tool developed by KDE people to handle DocBook XML. AFAIK, it was the first program to extract strings to translate from documentation to PO files, and inject them back after translation.

It can only handle XML, and only a particular DTD. I'm quite unhappy with the handling of lists, which end in one big msgid. When the list become big, the chunk becomes harder to swallow.

This program done by Denis Barbier is a sort of precursor of the po4a SGML module, which more or less deprecates it. As the name says, it handles only the DebianDoc DTD, which is more or less a deprecated DTD.
Used by the GIMP Documentation Team since 2004, works quite well even if, as the name suggests, only with XML files and needs specially configured makefiles.
The Sphinx Documentation Project also uses gettext extensively to manage its translations. Unfortunately, it works only for a few text formats, rest and markdown, although it is perhaps the only tool that does this managing the whole translation process.

The main advantages of po4a over them are the ease of extra content addition (which is even worse there) and the ability to achieve gettextization.

  • The translations are not stored along with the original, which makes it possible to detect if translations become out of date.
  • The translations are stored in separate files from each other, which prevents translators of different languages from interfering, both when submitting their patch and at the file encoding level.
  • It is based internally on gettext (but po4a offers a very simple interface so that you don't need to understand the internals to use it). That way, we don't have to re-implement the wheel, and because of their wide use, we can think that these tools are more or less bug free.
  • Nothing changed for the end-user (beside the fact translations will hopefully be better maintained). The resulting documentation file distributed is exactly the same.
  • No need for translators to learn a new file syntax and their favorite PO file editor (like Emacs' PO mode, Lokalize or Gtranslator) will work just fine.
  • gettext offers a simple way to get statistics about what is done, what should be reviewed and updated, and what is still to do. Some example can be found at those addresses:
    - https://docs.kde.org/stable5/en/kdesdk/lokalize/project-view.html
    - http://www.debian.org/intl/l10n/
    

But everything isn't green, and this approach also has some disadvantages we have to deal with.

  • Addenda are somewhat strange at the first glance.
  • You can't adapt the translated text to your preferences, like splitting a paragraph here, and joining two other ones there. But in some sense, if there is an issue with the original, it should be reported as a bug anyway.
  • Even with an easy interface, it remains a new tool people have to learn.

    One of my dreams would be to integrate somehow po4a to Gtranslator or Lokalize. When a documentation file is opened, the strings are automatically extracted, and a translated file + po file can be written to disk. If we manage to do an MS Word (TM) module (or at least RTF) professional translators may even use it.

Denis Barbier <barbier,linuxfr.org>
Martin Quinson (mquinson#debian.org)
2024-06-08 perl v5.38.2