Rename 'kohana' to 'system' to conform to the Kohana filesystem layout. I'm comfortable with us not clearly drawing the distinction about the fact that it's Kohana.

system/core/utf8/strlen.php

@@ -0,0 +1,21 @@
+<?php defined('SYSPATH') OR die('No direct access allowed.');
+/**
+ * utf8::strlen
+ *
+ * @package    Core
+ * @author     Kohana Team
+ * @copyright  (c) 2007 Kohana Team
+ * @copyright  (c) 2005 Harry Fuecks
+ * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt
+ */
+function _strlen($str)
+{
+	// Try mb_strlen() first because it's faster than combination of is_ascii() and strlen()
+	if (SERVER_UTF8)
+		return mb_strlen($str);
+
+	if (utf8::is_ascii($str))
+		return strlen($str);
+
+	return strlen(utf8_decode($str));
+}