Cacher is the code snippet organizer for pro developers

<?php

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

	return $join . "
		INNER JOIN " . $wpdb->term_relationships . " ON (R.`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)
	";
}
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;

	return $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 = " . $post_id . " )
	";
}
add_filter( 'bsearch_posts_where', 'filter_bsearch_posts_where' );