diff --git a/file/lib/data/message/MessageAction.class.php b/file/lib/data/message/MessageAction.class.php
index 7d8caf4..bc7d434 100644
--- a/file/lib/data/message/MessageAction.class.php
+++ b/file/lib/data/message/MessageAction.class.php
@@ -66,7 +66,7 @@ public function validateSend() {
 		$this->parameters['enableHTML'] = false;
 		
 		// validate text
-		if (\wcf\util\StringUtil::length($this->parameters['text']) > CHAT_MAX_LENGTH) throw new UserInputException('text', 'tooLong');
+		if (mb_strlen($this->parameters['text']) > CHAT_MAX_LENGTH) throw new UserInputException('text', 'tooLong');
 		
 		// search for disallowed bbcodes
 		$disallowedBBCodes = \wcf\system\bbcode\BBCodeParser::getInstance()->validateBBCodes($this->parameters['text'], explode(',', WCF::getSession()->getPermission('user.chat.allowedBBCodes')));
diff --git a/file/lib/page/ChatPage.class.php b/file/lib/page/ChatPage.class.php
index 76b339c..bbff697 100644
--- a/file/lib/page/ChatPage.class.php
+++ b/file/lib/page/ChatPage.class.php
@@ -147,7 +147,7 @@ public function readCommands() {
 		foreach ($files as $file) {
 			$command = $regex->replace(basename($file), '');
 			if ($command == 'Plain') continue;
-			$this->commands[] = \wcf\util\StringUtil::toLowerCase($command);
+			$this->commands[] = mb_strtolower($command);
 		}
 		
 		$this->commands = array_merge($this->commands, array_keys(\chat\system\command\CommandHandler::getAliasMap()));
diff --git a/file/lib/system/command/CommandHandler.class.php b/file/lib/system/command/CommandHandler.class.php
index c575e62..ed9e8b1 100644
--- a/file/lib/system/command/CommandHandler.class.php
+++ b/file/lib/system/command/CommandHandler.class.php
@@ -97,7 +97,7 @@ public function getRoom() {
 	 * @return	string
 	 */
 	public function getParameters() {
-		$parts = explode(' ', StringUtil::substring($this->text, StringUtil::length(static::COMMAND_CHAR)), 2);
+		$parts = explode(' ', mb_substr($this->text, mb_strlen(static::COMMAND_CHAR)), 2);
 		
 		if (!isset($parts[1])) return '';
 		return $parts[1];
@@ -107,7 +107,7 @@ public function getParameters() {
 	 * Loads the command.
 	 */
 	public function loadCommand() {
-		$parts = explode(' ', StringUtil::substring($this->text, StringUtil::length(static::COMMAND_CHAR)), 2);
+		$parts = explode(' ', mb_substr($this->text, mb_strlen(static::COMMAND_CHAR)), 2);
 		
 		$class = '\chat\system\command\commands\\'.ucfirst(strtolower($parts[0])).'Command';
 		if (!class_exists($class)) {
diff --git a/file/lib/system/command/commands/AwayCommand.class.php b/file/lib/system/command/commands/AwayCommand.class.php
index fb0eff0..3056b01 100644
--- a/file/lib/system/command/commands/AwayCommand.class.php
+++ b/file/lib/system/command/commands/AwayCommand.class.php
@@ -1,7 +1,6 @@
 <?php
 namespace chat\system\command\commands;
 use \wcf\system\WCF;
-use \wcf\util\StringUtil;
 
 /**
  * Marks the user as away.
diff --git a/file/lib/system/command/commands/ColorCommand.class.php b/file/lib/system/command/commands/ColorCommand.class.php
index f8263a1..1fe3245 100644
--- a/file/lib/system/command/commands/ColorCommand.class.php
+++ b/file/lib/system/command/commands/ColorCommand.class.php
@@ -1,6 +1,5 @@
 <?php
 namespace chat\system\command\commands;
-use \wcf\util\StringUtil;
 
 /**
  * Changes the color of the username
diff --git a/file/lib/system/command/commands/FreeCommand.class.php b/file/lib/system/command/commands/FreeCommand.class.php
index 6297d8f..97a88e8 100644
--- a/file/lib/system/command/commands/FreeCommand.class.php
+++ b/file/lib/system/command/commands/FreeCommand.class.php
@@ -14,7 +14,7 @@ class FreeCommand extends MeCommand {
 	public function __construct(\chat\system\command\CommandHandler $commandHandler) {
 		parent::__construct($commandHandler);
 		
-		if (\wcf\util\StringUtil::toLowerCase($this->commandHandler->getParameters()) != 'the fish') {
+		if (mb_strtolower($this->commandHandler->getParameters()) != 'the fish') {
 			throw new \InvalidArgumentException();
 		}
 		
diff --git a/file/lib/system/command/commands/InfoCommand.class.php b/file/lib/system/command/commands/InfoCommand.class.php
index b1f81eb..c51cccc 100644
--- a/file/lib/system/command/commands/InfoCommand.class.php
+++ b/file/lib/system/command/commands/InfoCommand.class.php
@@ -4,7 +4,6 @@
 use \wcf\data\user\User;
 use \wcf\system\WCF;
 use \wcf\util\DateUtil;
-use \wcf\util\StringUtil;
 
 /**
  * Shows information about the specified user.
diff --git a/file/lib/system/command/commands/MeCommand.class.php b/file/lib/system/command/commands/MeCommand.class.php
index 9d90113..c14be30 100644
--- a/file/lib/system/command/commands/MeCommand.class.php
+++ b/file/lib/system/command/commands/MeCommand.class.php
@@ -1,6 +1,5 @@
 <?php
 namespace chat\system\command\commands;
-use \wcf\util\StringUtil;
 
 /**
  * Indicates an action. The message is shown without the colon.
diff --git a/file/lib/system/command/commands/TemproomCommand.class.php b/file/lib/system/command/commands/TemproomCommand.class.php
index 76d4428..121e69e 100644
--- a/file/lib/system/command/commands/TemproomCommand.class.php
+++ b/file/lib/system/command/commands/TemproomCommand.class.php
@@ -1,7 +1,6 @@
 <?php
 namespace chat\system\command\commands;
 use \wcf\system\WCF;
-use \wcf\util\StringUtil;
 
 /**
  * Creates a temporary room
diff --git a/file/lib/util/ChatUtil.class.php b/file/lib/util/ChatUtil.class.php
index fa5c505..2cb9ea1 100644
--- a/file/lib/util/ChatUtil.class.php
+++ b/file/lib/util/ChatUtil.class.php
@@ -58,7 +58,7 @@ public static function getPackageID() {
 	 * @return	string
 	 */
 	public static function gradient($string, $start, $end) {
-		if (($length = \wcf\util\StringUtil::length($string)) === 0) return '';
+		if (($length = mb_strlen($string)) === 0) return '';
 		
 		if ($start === $end) {
 			return '<span style="color:rgb('.($start >> 16 & 255).','.($start >> 8 & 255).','.($start & 255).')">'.\wcf\util\StringUtil::encodeHTML($string).'</span>';
@@ -87,8 +87,8 @@ public static function gradient($string, $start, $end) {
 	 */
 	public static function str_split($string, $length = 1) {
 		$result = array();
-		for ($i = 0, $max = \wcf\util\StringUtil::length($string); $i < $max; $i += $length) {
-			$result[] = \wcf\util\StringUtil::substring($string, $i, $length);
+		for ($i = 0, $max = mb_strlen($string); $i < $max; $i += $length) {
+			$result[] = mb_substr($string, $i, $length);
 		}
 		return $result;
 	}