Plugin Polylang displays all posts

<?php
/*
Plugin Name: Polylang displays all posts
Version: 0.2
Author: F. Demarle
Description: Adds the possibility to display posts in all languages with Polylang. Requires Polylang v0.9.2
*/

/*
This plugin is no more maintained and is not compatible with recent versions of Polylang.
I keep it here in case someone wants to use it at a base for his own needs
*/

/*  Copyright 2012 F. Demarle

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License, published by
    the Free Software Foundation, either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

class pll_no_lang {
    protected $curlang;

    function __construct() {
        add_filter('pll_dropdown_language_args', array(&$this, 'pll_dropdown_language_args'));
        add_filter('pll_get_default_language', create_function('','return 0;'));
        add_filter('pll_get_objects_with_no_lang', create_function('','return false;'));

        // filters posts according to the language
        add_filter('pre_get_posts', array(&$this, 'pre_get_posts'), 20); // after polylang

        add_action('wp', array(&$this, 'wp'), 1); // before polylang

        // rewrites archives, next and previous post links to filter them by language
        foreach (array('getarchives', 'get_previous_post', 'get_next_post') as $filter)
            add_filter($filter.'_where', array(&$this, 'posts_where'), 1); // before polylang

        add_filter('terms_clauses', array(&$this, 'terms_clauses'), 20); // after polylang
    }

    // adds the item 'No language' for posts, media and terms
    function pll_dropdown_language_args($args) {
        if ((isset($args['name']) && $args['name'] == 'post_lang_choice') ||
            (isset($args['class']) && $args['class'] == 'media_lang_choice') ||
            (isset($args['name']) && $args['name'] == 'term_lang_choice'))
            $args['add_option'] = __('No language', 'polylang');
        return $args;
    }

    // return the array of all languages ids which are not $languages
    function invert_languages_ids($languages) {
        global $polylang;
        // get an array of ids for languages
        $languages = is_array($languages) ? $languages : array($languages);
        foreach ($languages as $key=>$lang)
            $languages[$key] = $polylang->get_language($lang)->term_id;

        // invert the array
        return array_diff($polylang->get_languages_list(array('fields' => 'ids')), $languages);
    }

    function pre_get_posts($query) {
        $qvars = $query->query_vars;
        if (is_admin() || !isset($qvars['lang']) /*|| (isset($qvars['pagename']) && $qvars['pagename'])*/)
            return;

        $query->set('tax_query', array(array(
            'taxonomy' => 'language',
            'fields'   => 'ids',
            'terms'    =>  $this->invert_languages_ids($qvars['lang']),
            'operator' => 'NOT IN'
        )));

        $this->curlang = $qvars['lang']; // remember the queried language
        unset ($query->query_vars['lang']); // to allow querying posts with no language
        $query->is_tax = false; // to avoid lot of errors
    }

    // so that Polylang knows the language to load
    function wp() {
        if (isset($this->curlang))
            set_query_var('lang', $this->curlang);
    }

    function posts_where($sql) {
        global $polylang, $wpdb;
        foreach (array('getarchives', 'get_previous_post', 'get_next_post') as $filter)
            foreach (array('_join', '_where') as $clause)
                remove_filter($filter.$clause, array(&$polylang, 'posts'.$clause));

        $p = current_filter() == 'getarchives_where' ? $wpdb->posts : 'p';
        $ids = implode(',', $this->invert_languages_ids($polylang->get_current_language()));

        return $sql . $wpdb->prepare(" AND ($p.ID NOT IN (
            SELECT object_id
            FROM $wpdb->term_relationships
            WHERE term_taxonomy_id IN ($ids)
        ))");
    }

    function terms_clauses($clauses) {
        preg_match('#pll_tm.meta_value IN \(([0-9]+)\)#', $clauses['where'], $matches);
        if (!empty($matches)) {
            global $wpdb;
            $where_lang = $wpdb->prepare("pll_tm.meta_key = '_language' AND pll_tm.meta_value IN (%d)", $matches[1]); // terms in the right language
            $where_none = $wpdb->prepare("t.term_id NOT IN (SELECT term_id FROM $wpdb->termmeta WHERE meta_key IN ('_language'))"); // terms with no language set
            $clauses['where'] = str_replace($where_lang, "(($where_lang) OR ($where_none))", $clauses['where']);
        }
        return $clauses;
    }
}

new pll_no_lang();

?>