Auto translate for Polylang

<?php
/*
Plugin name: auto translate for Polylang
*/

class Polylang_Auto_Translate {
    function __construct() {
        add_action('pre_get_posts', array(&$this, 'pre_get_posts')); // after Polylang
    }

    function pre_get_posts($query) {
        if (!$lang = pll_current_language())
            return;

        global $wpdb, $polylang;
        $qv = &$query->query_vars;

        $sign = create_function('$n', 'return $n > 0 ? 1 : ($n < 0 ? -1 : 0);');

        // /!\ always keep untranslated as is

        // term ids separated by a comma
        $arr = array();
        if (!empty($qv['cat'])) {
            foreach (explode(',', $qv['cat']) as $cat)
                $arr[] = ($tr = $sign($cat) * pll_get_term(abs($cat))) ? $tr : $cat;

            $qv['cat'] = implode(',', $arr);
        }

        // category_name
        $arr = array();
        if (!empty($qv['category_name'])) {
            foreach (explode(',', $qv['category_name']) as $slug)
                $arr[] = (($cat = get_category_by_slug($slug)) && ($tr_id = pll_get_term($cat->term_id)) && !is_wp_error($tr = get_category($tr_id))) ?
                    $tr->slug : $slug;

            $qv['category_name'] = implode(',', $arr);
        }

        // array of term ids
        foreach (array('category__and', 'category__in', 'category__not_in', 'tag__and', 'tag__in', 'tag__not_in') as $key) {
            $arr = array();
            if (!empty($qv[$key])) {
                foreach ($qv[$key] as $cat)
                    $arr[] = ($tr = pll_get_term($cat)) ? $tr : $cat;

                $qv[$key] = $arr;
            }
        }

        // tag
        $arr = array();
        if (!empty($qv['tag'])) {
            $sep = strpos($qv['tag'], ',') !== false ? ',' : '+'; // two possible separators for tag slugs
            foreach (explode($sep, $qv['tag']) as $slug)
                $arr[] = (($tag = get_term_by('slug', $slug, 'post_tag')) && ($tr_id = pll_get_term($tag->term_id)) && !is_wp_error($tr = get_tag($tr_id))) ?
                    $tr->slug : $slug;

            $qv['tag'] = implode($sep, $arr);
        }

        // tag_id can only take one id
        if (!empty($qv['tag_id']) && $tr_id = pll_get_term($qv['tag_id']))
            $qv['tag_id'] = $tr_id;


        // array of tag slugs
        foreach (array('tag_slug__and', 'tag_slug__in') as $key) {
            $arr = array();
            if (!empty($qv[$key])) {
                foreach ($qv[$key] as $slug)
                    $arr[] = (($tag = get_term_by('slug', $slug, 'post_tag')) && ($tr_id = pll_get_term($tag->term_id)) && !is_wp_error($tr = get_tag($tr_id))) ?
                        $tr->slug : $slug;

                $qv[$key] = $arr;
            }
        }

        // custom taxonomies
        // according to codex, this type of query is deprecated as of WP 3.1 but it does not appear in WP 3.5 source code
        foreach (array_diff($polylang->taxonomies, array('category', 'post_tag')) as $taxonomy) {
            $tax = get_taxonomy($taxonomy);
            $arr = array();
            if (!empty($qv[$tax->query_var])) {
                $sep = strpos($qv[$tax->query_var], ',') !== false ? ',' : '+'; // two possible separators
                foreach (explode($sep, $qv[$tax->query_var]) as $slug)
                    $arr[] = (($tag = get_term_by('slug', $slug, $taxonomy)) && ($tr_id = pll_get_term($tag->term_id)) && !is_wp_error($tr = get_term($tr_id, $taxonomy))) ?
                        $tr->slug : $slug;

                $qv[$tax->query_var] = implode($sep, $arr);
            }
        }

        // tax_query since WP 3.1
        if (!empty($qv['tax_query']) && is_array($qv['tax_query'])) {
            foreach ($qv['tax_query'] as $key => $q) {
                $arr = array();
                $field = empty($q['field']) ? 'id' : $q['field'];
                foreach (explode(',', $q['terms']) as $t)
                    $arr[] = (($tag = get_term_by($field, $t, $taxonomy)) && ($tr_id = pll_get_term($tag->term_id)) && !is_wp_error($tr = get_term($tr_id, $taxonomy))) ?
                        $tr->$field : $t;

                $qv['tax_query'][$key]['terms'] = implode(',', $arr);
            }
        }

        // p, page_id, post_parent can only take one id
        foreach (array('p', 'page_id', 'post_parent') as $key)
            if (!empty($qv[$key]) && $tr_id = pll_get_post($qv[$key]))
                $qv[$key] = $tr_id;

        // name, pagename can only take one slug
        foreach (array('name', 'pagename') as $key) {
            if (!empty($qv[$key])) {
                // no function to get post by name
                $post_type = empty($qv['post_type']) ? 'post' : $qv['post_type'];
                $id = $wpdb->get_var($wpdb->prepare("SELECT ID from $wpdb->posts WHERE post_type=%s AND post_name=%s", $post_type, $qv[$key]));
                $qv[$key] = ($id && ($tr_id = pll_get_post($id)) && $tr = get_post($tr_id)) ? $tr->post_name : $qv[$key];
            }
        }

        // array of post ids
        foreach (array('post__in', 'post__not_in') as $key) {
            $arr = array();
            if (!empty($qv[$key])) {
                foreach ($qv[$key] as $p)
                    $arr[] = ($tr = pll_get_post($p)) ? $tr : $p;

                $qv[$key] = $arr;
            }
        }
    }
}

add_action('pll_language_defined', create_function('', 'new Polylang_Auto_Translate();'));