If you are using this for more than one channel then you must remove the channel restriction.
Code:
raw USERNOTICE:*:{
  if ($msgtags(msg-id).key == resub) {
    var %nick $iif($msgtags(display-name).key, $v1, $msgtags(login).key)
    if ($0 == 1) {
      describe $1 %nick has been subbed for $msgtags(msg-param-months).key months in a row!
    }
    else {
      describe $1 %nick has been subbed for $msgtags(msg-param-months).key months in a row with the message: $qt($2-)
    }
  }
}