Polylang DB correction for duplicate tags and categories

<?php
/*
Plugin Name: Polylang database correction
*/

/*
Correct a the database when tags and/or categories are duplicated with Polylang activated (an not with Polylang deactivated)
See: http://wordpress.org/support/topic/plugin-polylang-categories-and-tags-are-duplicated
Polylang must be activated for this plugin to work

Make a backup of your database
Copy paste in a file correct.php
Upload the file in the plugins directory
Activate the plugin -> it should immediately remove duplicate tags and categories
Deactivate the plugin and delete it
*/

add_action('init', 'pll_correct_db', 100); // after Polylang
function pll_correct_db() {
    global $polylang, $wpdb;
    if (!isset($polylang))
        return;

    $meta_ids = $wpdb->get_col("SELECT meta_id FROM $wpdb->termmeta AS tm WHERE tm.meta_key = '_language'");
    $terms = $wpdb->get_col("SELECT term_id FROM $wpdb->termmeta AS tm WHERE tm.meta_key = '_language'");
    $unique = array_unique($terms, SORT_NUMERIC);
    foreach (array_keys(array_diff_key($terms, $unique)) as $key)
        $to_correct[] = $meta_ids[$key];

    if (isset($to_correct)) {
        $query = $wpdb->prepare("DELETE FROM $wpdb->termmeta WHERE meta_id IN( ". implode( ',', $to_correct ) ." )");
        $wpdb->query($query);
    }
}