Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 4010)
+++ wp-includes/formatting.php	(working copy)
@@ -149,6 +149,9 @@
 }
 
 function remove_accents($string) {
+	if ( !preg_match('/[\x80-\xff]/', $string) )
+		return $string;
+
 	if (seems_utf8($string)) {
 		$chars = array(
 		// Decompositions for Latin-1 Supplement