doc/plugins/po.mdwn



[[!template id=plugin name=po core=0 author="[[intrigeri]]"]]
[[!tag type/format]]
This plugin adds support for multi-lingual wikis, translated with
gettext, using po4a.
It depends on the Perl Locale::Po4a::Po library (apt-get install po4a).
Introduction
A language is chosen as the "master" one, and any other supported
language is a "slave" one.
A page written in the "master" language is a "master" page. It can be
of any page type supported by ikiwiki, except po. It does not have to be
named a special way: migration to this plugin does not imply any page
renaming work.
Example: bla/page.mdwn is a "master" Markdown page written in
English; if usedirs is enabled, it is rendered as
bla/page/index.en.html, else as bla/page.en.html.
Any translation of a "master" page into a "slave" language is called
a "slave" page; it is written in the gettext PO format. po is now
a page type supported by ikiwiki.
Example: bla/page.fr.po is the PO "message catalog" used to
translate bla/page.mdwn into French; if usedirs is enabled, it is
rendered as bla/page/index.fr.html, else as bla/page.fr.html
Configuration
Supported languages
po_master_language is used to set the "master" language in
ikiwiki.setup, such as:
    po_master_language => { 'code' => 'en', 'name' => 'English' }

po_slave_languages is used to set the list of supported "slave"
languages, such as:
    po_slave_languages => { 'fr' => 'Français',
                            'es' => 'Castellano',
                            'de' => 'Deutsch',
    }

Decide which pages are translatable
The po_translatable_pages setting configures what pages are
translatable. It is a [[ikiwiki/PageSpec]], so you have lots of
control over what kind of pages are translatable.
The .po files are not considered as being translatable, so you don't need to
worry about excluding them explicitly from this [[ikiwiki/PageSpec]].
Internal links
The po_link_to option in ikiwiki.setup is used to decide how
internal links should be generated, depending on web server features
and site-specific preferences.
Default linking behavior
If po_link_to is unset, or set to default, ikiwiki's default
linking behavior is preserved: \[[destpage]] links to the master
language's page.
Link to current language
If po_link_to is set to current, \[[destpage]] links to the
destpage's version written in the current page's language, if
available, i.e.:

foo/destpage/index.LL.html if usedirs is enabled
foo/destpage.LL.html if usedirs is disabled

Link to negotiated language
If po_link_to is set to negotiated, \[[page]] links to the
negotiated preferred language, i.e. foo/page/.
(In)compatibility notes:

if usedirs is disabled, it does not make sense to set po_link_to
to negotiated; this option combination is neither implemented
nor allowed.
if the web server does not support Content Negotiation, setting
po_link_to to negotiated will produce a unusable website.

Server support
Apache
Using Apache mod_negotiation makes it really easy to have Apache
serve any page in the client's preferred language, if available.
This is the default Debian Apache configuration.
When usedirs is enabled, one has to set DirectoryIndex index for
the wiki context.
Setting DefaultLanguage LL (replace LL with your default MIME
language code) for the wiki context can help to ensure
bla/page/index.en.html is served as Content-Language: LL.
lighttpd
lighttpd unfortunately does not support content negotiation.
FIXME: does mod_magnet provide the functionality needed to
emulate this?
Usage
Templates
The ISTRANSLATION and ISTRANSLATABLE variables can be used to
display things only on translatable or translation pages.
Display page's versions in other languages
The OTHERLANGUAGES loop provides ways to display other languages'
versions of the same page, and the translations' status.
One typically adds the following code to templates/page.tmpl:
<TMPL_IF NAME="OTHERLANGUAGES">
<div id="otherlanguages">
  <ul>
  <TMPL_LOOP NAME="OTHERLANGUAGES">
    <li>
      <a href="<TMPL_VAR NAME="URL">"><TMPL_VAR NAME="LANGUAGE"></a>
      <TMPL_UNLESS NAME="MASTER">
        (<TMPL_VAR NAME="PERCENT">&nbsp;%)
      </TMPL_UNLESS>
    </li>
  </TMPL_LOOP>
  </ul>
</div>
</TMPL_IF>

The following variables are available inside the loop (for every page in):

URL - url to the page
CODE - two-letters language code
LANGUAGE - language name (as defined in po_slave_languages)
MASTER - is true (1) if, and only if the page is a "master" page
PERCENT - for "slave" pages, is set to the translation completeness, in percents

Display the current translation status
The PERCENTTRANSLATED variable is set to the translation
completeness, expressed in percent, on "slave" pages.
One can use it this way:
<TMPL_IF NAME="ISTRANSLATION">
<div id="percenttranslated">
  <TMPL_VAR NAME="PERCENTTRANSLATED">
</div>
</TMPL_IF>

Additional PageSpec tests
This plugin enhances the regular [[ikiwiki/PageSpec]] syntax with some
additional tests that are documented [[here|ikiwiki/pagespec/po]].
Automatic PO file update
Committing changes to a "master" page:

updates the POT file and the PO files for the "slave" languages;
the updated PO files are then put under version control;
triggers a refresh of the corresponding HTML slave pages.

Also, when the plugin has just been enabled, or when a page has just
been declared as being translatable, the needed POT and PO files are
created, and the PO files are checked into version control.
Discussion pages
Discussion should happen in the language in which the pages are
written for real, i.e. the "master" one. If discussion pages are
enabled, "slave" pages therefore link to the "master" page's
discussion page.
Translating
One can edit the PO files using ikiwiki's CGI (a message-by-message
interface could also be implemented at some point).
If [[tips/untrusted_git_push]] is setup, one can edit the PO files in one's
preferred $EDITOR, without needing to be online.
TODO
Security checks

Can any sort of directives be put in po files that will
cause mischief (ie, include other files, run commands, crash gettext,
whatever).
Any security issues on running po4a on untrusted content?

gettext/po4a rough corners

fix infinite loop when synchronizing two ikiwiki (when checkouts
live in different directories): say bla.fr.po has been updated in
repo2; pulling repo2 from repo1 seems to trigger a PO update, that
changes bla.fr.po in repo1; then pushing repo1 to repo2 triggers
a PO update, that changes bla.fr.po in repo2; etc.; fixed in
629968fc89bced6727981c0a1138072631751fee?
new translations created in the web interface must get proper
charset/encoding gettext metadata, else the next automatic PO update
removes any non-ascii chars; possible solution: put such metadata
into the Pot file, and let it propagate; should be fixed in
773de05a7a1ee68d2bed173367cf5e716884945a, time will tell.

Misc. improvements
page titles
Use nice page titles from meta plugin in links, as inline already
does. This is actually a duplicate for
[[bugs/pagetitle_function_does_not_respect_meta_titles]], which might
be fixed by something like [[todo/using_meta_titles_for_parentlinks]].
backlinks
po_link_to = negotiated
If a given translatable sourcepage.mdwn links to [[destpage]],
sourcepage.LL.po also link to [[destpage]], and the latter has the
master page and all its translations listed in the backlinks. On the
other hand, translations of destpage get none of these backlinks.
What would be nice is:

if a translatable page links to another translatable page: the
master destpage gets a backlink to the master sourcepage, and every
slave destpage gets a backlink to the corresponding slave sourcepage
if a translatable page links to a non-translatable page: the
destpage gets a backlink to the master sourcepage only
if a non-translatable page links to a translatable page: every
master or slave destpage gets a backlink to the sourcepage
if a non-translatable page links to another non-translatable page:
the default behavious is nice, don't change it

po_link_to = current
At first glance, backlinks seem to work nicely, but a more thorough
look is needed.
po_link_to = default
FIXME
Translation quality assurance
Modifying a PO file via the CGI must be forbidden if the new version
is not a valid PO file. As a bonus, check that it provides a more
complete translation than the existing one.
A new cansave type of hook would be needed to implement this.
Note: committing to the underlying repository is a way to bypass
this check.