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 => { '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](http://httpd.apache.org/docs/2.2/content-negotiation.html).

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:

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|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.

Self links
----------

If a page contains a WikiLink to itself, ikiwiki does not normally
turn that into a hyperlink. However, if a translated page contains a
WikiLink to itself, a hyperlink is inserted, at least with the default
`po_link_to` the link points to the English version of the page. Is there a
good reason for that to be done? --[[Joey]]

> The commit 0113c69d4fb in my po branch might fix this. --[[intrigeri]]

>> It may fix it in passing, but shouldn't it also be fixed for the other
>> `po_link_to` styles?

>>> Other `po_link_to` styles already work ok: say there is
>>> a \[[dest]] link on a page called `dest`. When rendering
>>> `dest.LL`, `mybestlink` returns `dest.LL`, and `htmllink` is then
>>> able to detect, and manage correctly, that it is a self-link.
>>> --[[intrigeri]]

>> (Also, if `mybestlink` is going to always just return `bestlink` in
>> this case, there seems no reason to inject it.) --[[Joey]]

>>> Right. Commit cdc3576c8d1efb2 in my po branch prevents
>>> `mybestlink` to be injected when `po_link_to` is
>>> `default`. --[[intrigeri]]

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]] 

Duplicate %links ?
------------------

I notice code in the scan hook that seems to assume
that %links will accumulate duplicate links for a page.
That used to be so, but the bug was fixed. Does this mean
that po might be replacing the only link on a page, in error? 
--[[Joey]] 

> It would replace it. The only problematic case is when another
> plugin has its own reasons, in its `scan` hook, to add a page
> that is already there to `$links{$page}`. This other plugin's
> effect might then be changed by po's `scan` hook... which could
> be either good (better overall l10n) or bad (break the other
> plugin's goal). --[[intrigeri]]

>> Right.. well, the cases where links are added is very small.
>> Grepping for `add_link`, it's just done by link, camelcase, meta, and
>> tag. All of these are supposed to work just link regular links
>> so I'd think that is ok. We could probably remove the currently scary
>> comment about only wanting to change the first link. --[[Joey]] 

>>> Commit 3c2bffe21b91684 in my po branch does this. --[[intrigeri]]

Name of toplevel index page
---------------------------

Normally at the top index page of a wiki, you see the wiki name at
the top. However, at the top *translated* index page, you see something
like "index.da". --[[Joey]]

> I suggest changing `Render.pm`, line 115, to replace the `$page eq 'index'`
> test with a predicate call such as isindexpage($page). Such a predicate
> function could then be overriden by the po plugin. --[[intrigeri]]

>> Could do that, but if you have such a function it's natural to want to
>> use it elsewhere. Not clear to me it would make sense for po to override
>> such a function if it were used in some of the other places that compare
>> to index.
>> 
>> The other option would be for po to override the template setting.
>> --[[Joey]] 

>>> Great idea. Commit 6c0f9c691c3df3a in my po branch does it. --[[intrigeri]]

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.

Documentation
-------------

Maybe write separate documentation depending on the people it targets:
translators, wiki administrators, hackers. This plugin may be complex
enough to deserve this.