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+[[!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
+---------
+
+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 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.
+
+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 her
+preferred `$EDITOR`, without needing to be online.
+
+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 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
+------------------
+
+### preview
+
+preview does not work for PO files.
+
+### automatic POT/PO update
+
+Use the `change` hook instead of `needsbuild`?
+
+### 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]].
+
+### websetup
+
+Which configuration settings are safe enough for websetup?
+
+### parentlinks
+
+When the wiki home page is translatable, the parentlinks plugin sets
+`./index.html` as its translations' single parent link. Ideally, the home page's
+translations should get no parent link at all, just like the version written in
+the master language.
+
+### backlinks
+
+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.
+
+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.