Better Search and Polylang compatibility

better-search-polylang.php

<?php

// Doesn't work.

/**
 * Joins the taxonomy tables. Filters bsearch_posts_join.
 *
 * @param string $join
 * @return string
 */
function filter_bsearch_posts_join( $join ) {
	global $wpdb;

	$join .= "
		INNER JOIN {$wpdb->term_relationships} ON ({$wpdb->posts}.post_id = {$wpdb->term_relationships}.object_id)
		INNER JOIN {$wpdb->term_taxonomy} ON ({$wpdb->term_relationships}.term_taxonomy_id = {$wpdb->term_taxonomy}.term_taxonomy_id)
	";
	return $join;
}
add_filter( 'bsearch_posts_join', 'filter_bsearch_posts_join' );

/**
 * Select posts from the same language. Filters bsearch_posts_where.
 *
 * @param string $where
 * @return string
 */
function filter_bsearch_posts_where( $where ) {
	global $wpdb;

	$where .= "
		AND {$wpdb->term_taxonomy}.taxonomy = 'language'
		AND {$wpdb->term_taxonomy}.term_id IN ( SELECT TT.term_id FROM {$wpdb->term_taxonomy} TT INNER JOIN {$wpdb->term_relationships} TR ON TR.term_taxonomy_id = TT.term_taxonomy_id WHERE TR.object_id = {$wpdb->ID} )
	";
	return $where;
}
add_filter( 'bsearch_posts_where', 'filter_bsearch_posts_where' );