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, and is
written in any supported format but PO. It does not have to be named
a special way: migration from/to this plugin does not imply heavy
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
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' => { 'name' => 'Français', },
                            'es' => { 'name' => 'Castellano', },
                            'de' => { 'name' => 'Deutsch', }
    }

Decide which pages are translatable
The subset of "master" pages subject to translation is configurable:

a [[!translatable ]] directive, when put on a page, makes it
translatable
to set at once a bunch of pages as being translatable, use this
[[ikiwiki/directive]] with the match=PageSpec argument.

Internal links
One can use the po_link_to_ option in ikiwiki.setup to choose 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: [[page]] links to the master
language's page.
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:

po_link_to => negotiated provides no useful behavior if usedirs
is disabled; this option combination is neither implemented nor
allowed
po_link_to => negotiated provides no useful behavior if the web
server does not support Content Negotiation

Link to current language
If po_link_to is set to current and the destination page is either
a translatable page or a translation, [[page]] links to the current
page's language, i.e.:

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

Server support
Apache
Using mod_negotiation makes it really easy to have Apache serve the
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) for the wiki context can be needed, to ensure
bla/page/index.en.html is served as Content-Language: LL.
FIXME: is it still needed with the new .en.html naming convention?
lighttpd
lighttpd unfortunately does not support content negotiation.
FIXME: does mod_magnet provide the functionality needed to
emulate this?
TODO
Optimization
Move match_istranslation and match_istranslatable code into helper
functions, and pre-compute what can be early in the build process:

the list of translatable (master) pages
for every translatable page, the list of slave pages

Display available translations
The [[linguas|plugins/contrib/linguas]] plugin has some code that can
be used as a basis to display the existing translations, and allow to
navigate between them.
View translation status
One should be able to view some information about the translation
completeness, either for a given page or for the whole wiki.
This should not be too hard using gettext tools. If this is
implemented as a
[[HTML::Template|http://search.cpan.org/search?mode=dist&query=HTML%3A%3ATemplate]]
loop, a page using it should depend on any "master" and "slave" pages
whose status is being displayed.
Automatic PO files update
Committing changes to a "master" page must:

update the POT file and the PO files for the supported languages,
before putting them under version control
trigger a refresh of the corresponding HTML slave pages

The former is to be done at a time when:

we know which "master" page was modified, and thus, which POT/PO
files have to be updated: the needsbuild hook is the first one to
run that provides us with the necessary information
we can modify the list of pages needing a refresh; this is
needsbuild hook's job

The latter can be implemented by making any "slave" page depend on the
corresponding "master" page. The add_depends function can achieve
this, if used in a FIXME hook.
UI consistency: rename "Edit" button on slave pages
It may be surprising to some, after having pressed Edit on a wiki
page, to end up editing a strange looking PO file. The Edit button
displayed on "slave" pages must therefore be renamed Improve
translation .
Pages selection depending on language
To improve user navigation in a multi-lingual wiki, site developers
must be enabled to write:
    \[[!map pages="dev/* and lang(LL)" feeds="no"]]

    \[[!map pages="dev/* and currentlang()" feeds="no"]]

Translation quality assurance
Modifying a PO file via the CGI must only be allowed if the new
version is 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.
Translating online
As PO is a wiki page type, we already have an online PO editor, that
is ikiwiki's CGI.
A message-by-message interface could also be implemented at some
point; a nice way to do offline translation work (without VCS access)
still has to be offered, though.
Translating offline without VCS access
The following workflow should be made possible for translators without
VCS access who need to edit the PO files in another editor than a web
browser:

download the page's PO file
use any PO editor to update the translation
upload the updated PO file

Implementation note: a generic mechanism to upload a page's source is
needed: it's only an alternative way to allow saving a the modified
page's source with the CGI.
Short-term workflow
A possible workaround is:

pretend to edit the PO file online
copy the PO file content from the textarea
cancel the edit
paste the content into a local file.
edit the local file in any PO editor
pretend to edit the PO file online
paste the modified local file's content into the edit textarea
save