path: root/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).
As detailed bellow in the security section, po4a is subject to
denial-of-service attacks before version 0.35.
[[!toc levels=2]]
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
(In)Compatibility
This plugin does not support the indexpages mode. If you don't know
what it is, you probably don't care.
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' => 'Español',
                            '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
Links targets
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.
Add 'Options MultiViews' to the wiki directory's configuration in Apache.
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.
For details, see Apache's documentation.
lighttpd
lighttpd unfortunately does not support content negotiation.
FIXME: does mod_magnet provide the functionality needed to
emulate this?
Usage
Templates
When po_link_to is not set to negotiated, one should replace some
occurrences of BASEURL with HOMEPAGEURL to get correct links to
the wiki homepage.
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.
An example of its use can be found in the default
templates/page.tmpl. In case you want to customize it, 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. It is used by
the default templates/page.tmpl.
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 and other sub-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.
Likewise, "slave" pages are not supposed to have sub-pages;
[[WikiLinks|wikilink]] that appear on a "slave" page therefore link to
the master page's sub-pages.
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.
Markup languages support
[[Markdown|mdwn]] is well supported. Some other markup languages supported
by ikiwiki mostly work, but some pieces of syntax are not rendered
correctly on the slave pages:

[[reStructuredText|rst]]: anonymous hyperlinks and internal
cross-references
[[wikitext]]: conversion of newlines to paragraphs
[[creole]]: verbatim text is wrapped, tables are broken
[[html]] and LaTeX: not supported yet; the dedicated po4a modules
could be used to support them, but they would need a security audit
other markup languages have not been tested.

Security
[[po/discussion]] contains a detailed security analysis of this plugin
and its dependencies.
When using po4a older than 0.35, it is recommended to uninstall
Text::WrapI18N (Debian package libtext-wrapi18n-perl), in order to
avoid a potential denial of service.
TODO
Better links
Once the fix to
[[bugs/pagetitle_function_does_not_respect_meta_titles]] from
[[intrigeri]]'s meta branch is merged into ikiwiki upstream, the
generated links' text will be optionally based on the page titles set
with the [[meta|plugins/meta]] plugin, and will thus be translatable.
It will also allow displaying the translation status in links to slave
pages. Both were implemented, and reverted in commit
ea753782b222bf4ba2fb4683b6363afdd9055b64, which should be reverted
once [[intrigeri]]'s meta branch is merged.
An integration branch, called meta-po, merges [[intrigeri]]'s po
and meta branches, and thus has this additional features.
Language display order
Jonas pointed out that one might want to control the order that links to
other languages are listed, for various reasons. Currently, there is no
order, as po_slave_languages is a hash. It would need to be converted
to an array to support this. (If twere done, twere best done quickly.)
--[[Joey]]
Pagespecs
I was suprised that, when using the map directive, a pagespec of "*"
listed all the translated pages as well as regular pages. That can
make a big difference to an existing wiki when po is turned on,
and seems generally not wanted.
(OTOH, you do want to match translated pages by
default when locking pages.) --[[Joey]]
Edit links on untranslated pages
If a page is not translated yet, the "translated" version of it
displays wikilinks to other, existing (but not yet translated?)
pages as edit links, as if those pages do not exist.
That's really confusing, especially as clicking such a link
brings up an edit form to create a new, english page.
This is with po_link_to=current or negotiated. With default, it doesn't
happen..
Also, this may only happen if the page being linked to is coming from an
underlay, and the underlays lack translation to a given language.
--[[Joey]]
Double commits of po files
When adding a new english page, the po files are created, committed,
and then committed again. The second commit makes this change:
-"Content-Type: text/plain; charset=utf-8\n"
-"Content-Transfer-Encoding: ENCODING"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: ENCODING\n"

Same thing happens when a change to an existing page triggers a po file
update. --[[Joey]]
Ugly messages with empty files
If there are empty .mdwn files, the po plugin displays some ugly messages.
Translation of directives
If a translated page contains a directive, it may expand to some english
text, or text in whatever single language ikiwiki is configured to "speak".
Maybe there could be a way to switch ikiwiki to speaking another language
when building a non-english page? Then the directives would get translated.
Created page type
The interdiction to create pages of type po was broken by the new
page_types code. This is fixed in my po branch by
commit 1914ae2fd24e1e802.
While I was there, I also added some code to set a new default value
to the type select field in case it was previously set to "po".
This code favors the type of the linking page's masterpage on page
creation (when from=page.LL). This is commit c9301d2c296f682.
--[[intrigeri]]
Documentation
Maybe write separate documentation depending on the people it targets:
translators, wiki administrators, hackers. This plugin may be complex
enough to deserve this.