how do I download an attachment with a Russian name?

how do I download an attachment with a Russian name? error when filename in Russian

<?php
set_time_limit(3000);
$hostname = '{imap.ukr.net:993/imap/ssl/novalidate-cert}INBOX';
$username = ''; # например somebody@gmail.com
$password = '';
$inbox = imap_open($hostname,$username,$password) or die('Cannot connect to Gmail: ' . imap_last_error());
$emails = imap_search($inbox,'ALL');
$max_emails = 16;
if($emails) {
    $count = 1;
     rsort($emails);
     foreach($emails as $email_number)
    {
        /* get information specific to this email */                
        $overview = imap_fetch_overview($inbox,$email_number,0);
        /* get mail message */
        $message = imap_fetchbody($inbox,$email_number,2);
        /* get mail structure */
        $structure = imap_fetchstructure($inbox, $email_number);
        $attachments = array();
        /* if any attachments found... */
        if(isset($structure->parts) && count($structure->parts))
        {
            for($i = 0; $i < count($structure->parts); $i++)
            {
                $attachments[$i] = array(
                    'is_attachment' => false,
                    'filename' => '',
                    'name' => '',
                    'attachment' => ''
                );
                if($structure->parts[$i]->ifdparameters)
                {
                    foreach($structure->parts[$i]->dparameters as $object)
                    {
                        if(strtolower($object->attribute) == 'filename')
                        {
                            $attachments[$i]['is_attachment'] = true;
                            $attachments[$i]['filename'] = $object->value;
                        }
                    }
                }
                if($structure->parts[$i]->ifparameters)
                {
                    foreach($structure->parts[$i]->parameters as $object)
                    {
                        if(strtolower($object->attribute) == 'name')
                        {
                            $attachments[$i]['is_attachment'] = true;
                            $attachments[$i]['name'] = $object->value;
                        }
                    }
                }
                if($attachments[$i]['is_attachment'])
                {
                    $attachments[$i]['attachment'] = imap_fetchbody($inbox, $email_number, $i+1);
                    /* 4 = QUOTED-PRINTABLE encoding */
                if($structure->parts[$i]->encoding == 3)
                    {
                        $attachments[$i]['attachment'] = base64_decode($attachments[$i]['attachment']);
                    }
                    /* 3 = BASE64 encoding */   
                 elseif($structure->parts[$i]->encoding == 4)
                    {
                        $attachments[$i]['attachment'] = quoted_printable_decode($attachments[$i]['attachment']);
                    } 
                }
        }
        }
        /* iterate through each attachment and save it */
        foreach($attachments as $attachment)
        {
            if($attachment['is_attachment'] == 1)
            {
                $filename = $attachment['name'];
            if(empty($filename)) $filename = $attachment['filename'];
                if(empty($filename)) $filename = time() . "dat";
                /* prefix the email number to the filename in case two emails
                 * have the attachment with the same file name.
                 */
     $fp = fopen('/mnt/c/1/'. $filename, "w+");
             fwrite($fp, $attachment['attachment']);
                fclose($fp);
            }
        }
        if($count++ >= $max_emails) break;
    }
}

imap_close($inbox);
echo "Done";
?>