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`).

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:

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
----------------

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
--------------------------

- commiting a new master page version updates the translations, but
  does not refresh recentchanges anymore after having checked-in the
  new translations (since manual IkiWiki::refresh() call was removed,
  I guess)
- 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.

`po_link_to = current`: seems to work nicely

### parentlinks

When `usedirs` is disabled and the home page is translatable, the
parent link to the wiki home page is broken (`/index.html`).

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.