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](http://po4a.alioth.debian.org/).

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: en|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, you should also set `DirectoryIndex index`.

These settings are also recommended, in order to avoid serving up rss files
as index pages:

	AddType application/rss+xml;qs=0.8 .rss
	AddType application/atom+xml;qs=0.8 .atom

For details, see [Apache's documentation](http://httpd.apache.org/docs/2.2/content-negotiation.html).

lighttpd
--------

Recent versions of lighttpd should be able to use
`$HTTP["language"]` to configure the translated pages to be served.

See [Lighttpd Issue](http://redmine.lighttpd.net/issues/show/1119)

TODO: Example

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.

The `LANG_CODE` and `LANG_NAME` variables can respectively be used to
display the current page's language code and pretty name.

### 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:

1. updates the POT file and the PO files for the "slave" languages;
   the updated PO files are then put under version control;
2. 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|ikiwiki/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]] and [[html]] are 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
* LaTeX: not supported yet; the dedicated po4a module
  could be used to support it, but it 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.

BUGS
====

[[!inline pages="bugs/po:* and !bugs/done and !link(bugs/done) and !bugs/*/*"
feeds=no actions=no archive=yes show=0]]

TODO
====

[[!inline pages="todo/po:* and !todo/done and !link(todo/done) and !todo/*/*"
feeds=no actions=no archive=yes show=0]]