title: Call to undefined function yii\helpers\mb_strlen() on PHP in Yii2 Framework
body: <p>I have an error occurred when i try run my project at the server.</p>
  
  <p>It could not defined mb_strlen() in /var/www/html/amhadm/vendor/yiisoft/yii2/helpers/BaseStringHelper.php</p>
  
  <p>Here is my code in BaseStringHelper.php</p>
  
  <pre><code> public static function basename($path, $suffix = '')
  {
      if (($len = mb_strlen($suffix)) &gt; 0 &amp;&amp; mb_substr($path, -$len) == $suffix) {
          $path = mb_substr($path, 0, -$len);
      }
      $path = rtrim(str_replace('\\', '/', $path), '/\\');
      if (($pos = mb_strrpos($path, '/')) !== false) {
          return mb_substr($path, $pos + 1);
      }
  
      return $path;
  }
  </code></pre>
  
  <p>Can someone guide me how to solve this problem ?</p>