I want to use codeigniter foreign character library in my custom PHP project how i can use it?

foreach( $foreign_characters as $replace => $with )
{
    $string = preg_replace($replace, $with, $string);
}

class Replacer
{
    /**
     * List of character replacements
     */
    static $foreign_characters = array(
        '/ä|æ|?/' => 'ae',
        '/ö|œ/' => 'oe',
        '/ü/' => 'ue',
        '/Ä/' => 'Ae',
        '/Ü/' => 'Ue',
        '/Ö/' => 'Oe',
        '/À|Á|Â|Ã|Ä|Å|?|?|?|?|?|?|?|?|?|?|?|?|?|?|?|?|?|?|?/' => 'A',
        '/à|á|â|ã|å|?|?|?|?|?|ª|?|?|?|?|?|?|?|?|?|?|?|?|?|?|?/' => 'a',
        );

    /**
     * Replaces all foreign characters listed in 
     * self::$foreign_characters with their given counterparts
     * @param $string string to replace characters in
     */
    public static function replace_chars_in($string)
    {
        foreach( self::$foreign_characters as $replace => $with )
        {
            $string = preg_replace($replace, $with, $string);
        }

        return $string;
    }
}

echo Replacer::replace_chars_in("äÄfäüädasÖä?asd");

function convert_accented_characters($str)
{
    static $array_from, $array_to;

    if ( ! is_array($array_from))
    {
        if (file_exists(APPPATH.'config/foreign_chars.php'))
        {
            include(APPPATH.'config/foreign_chars.php');
        }

        if (file_exists(APPPATH.'config/'.ENVIRONMENT.'/foreign_chars.php'))
        {
            include(APPPATH.'config/'.ENVIRONMENT.'/foreign_chars.php');
        }

        if (empty($foreign_characters) OR ! is_array($foreign_characters))
        {
            $array_from = array();
            $array_to = array();

            return $str;
        }

        $array_from = array_keys($foreign_characters);
        $array_to = array_values($foreign_characters);
    }

    return preg_replace($array_from, $array_to, $str);
}