ikiwiki/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, but 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 translations files are anyway 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
---------

### 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.

Additional PageSpec tests
-------------------------

This plugin enhances the regular [[ikiwiki/PageSpec]] syntax with some
additional tests that are documented [[here|ikiwiki/pagespec/po]].

Automatic PO files update
-------------------------

Committing changes to a "master" page:

1. updates the POT file and the PO files for the supported languages
   (this is done in the `needsbuild` hook); the updated PO files are
   then put under version control
2. triggers a refresh of the corresponding HTML slave pages (this is
   achieved by making any "slave" page dependent on the corresponding
   "master" page, in the `needsbuild` hook)

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.

TODO
====

OTHERLANGUAGES dependencies
---------------------------

Pages using `OTHERLANGUAGES` depend on any "master" and "slave" pages
whose status is being displayed. It is supposed to trigger dependency
loops, but no practical bugs were noticed yet.

Should pages using the `OTHERLANGUAGES` template loop be declared as
linking to the same page in other versions? To be rigorous, they
should, but this may clutter the backlinks.

Security checks
---------------

- `refreshpofiles` uses `system()`, whose args have to be checked more
  thoroughly to prevent any security issue (command injection, etc.).
- `refreshpofiles` and `refreshpot` create new files; this may need
  some checks, e.g. using `IkiWiki::prep_writefile()`

gettext/po4a rough corners
--------------------------

- fix the duplicated PO header mysterious bug
- fix the "duplicate message definition" error when updating a PO
  file; do PO files need normalizing? (may be a side effect of
  previous bug)

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.

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