$lang = array(
   'htmlTitle' => 'Тра-та-та'
);

class Lang {
   static private $data = array();
   static private $languageName = 'ua';
   static private $languagesList = array('ua', 'ru', 'en');
   
   private function __construct($value) {
      if (!in_array($value, self :: $languagesList)) {
         $value = self :: $languageName;
      } else {
         self :: $languageName = $value;
      }
      $languageFileLocation = './Include/Language/' . $value . '/Texts.php';
      require_once $languageFileLocation;
      self :: $data = $lang;
   }
   
   public static function setLang($value) {
      new self($value);
   }
   
   static public function get($value) {
      if (isset(self :: $data[$value])) { 
         return self :: $data[$value];
      } else {
         return 'undefined';
      }
   }
   static public function getLanguageName() {
      return self :: $languageName;
   }
}

...
Lang :: setLang('ua');
echo Lang :: get('htmlTitle');
...