This seems the correct way to encode ftp url which you could provide for your users:

function ftp_url_encode($string) {

   $hex="";
   $retstr = "";
   for ($i=0; $i < strlen($string) ;$i++) {

     $char = $string[$i];
     if(($char >= '0' && $char <= '9') || ($char >= 'A' && $char <= 'Z') || ($char >= 'a' && $char <= 'z') || $char == '.' || $char == '-' || $char == '/' || (ord($char) >=128) ) $retstr .= $char;
     else
     $retstr .= "%".strtoupper(dechex(ord($string[$i])));

   }
   return $retstr;
} 

Browsers mangle certain language characters