Index: taxonomy.php
===================================================================
--- taxonomy.php	(revision 15382)
+++ taxonomy.php	(working copy)
@@ -1104,7 +1104,8 @@
 
 	$term = trim( stripslashes( $term ) );
 
-	if ( '' === $slug = sanitize_title($term) )
+	$slug = sanitize_title($term,'');
+	if ( '' === apply_filters( 'pre_insert_term', $term, $taxonomy ) )
 		return 0;
 
 	$where = 't.slug = %s';