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, 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', }
        }


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
====

Links
-----

Choice between two behaviors must be possible in `ikiwiki.setup`;
a `po_link_to_current_language` option must allow switching
between them.

If `po_link_to_current_language` is disabled, `[[page]]` links to the
negotiated preferred language, i.e.:

- `usedirs` enabled: `bla/page/`
- `usedirs` disabled: `bla/page`

This obviously does not work in case Content Negotiation is not
supported by the web server, hence one can enable
`po_link_to_current_language` to make `[[page]]` link to the current
page's language, i.e.:

- `usedirs` enabled: `bla/page/index.LL.html`
- `usedirs` disabled: `bla/page.LL.html`

**FIXME**: should `po_link_to_current_language` be enabled by default?

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.

Decide which pages are translatable
-----------------------------------

The subset of "master" pages subject to translation must be
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.

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

Committing changes to a "master" page must:

1. update the POT file and the PO files for the supported languages,
   before putting them under version control
2. 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