Why don't you use a for statement and arrays. Rather than all those if statement you only need one and you can then use Array[i].length for the length of the string rather than specifying a number.
EDIT: I thought I might help you out by giving you an example of what I was trying to say incase you didn't understand. I just fixed up the code that you had posted.
code:
*/
var hi = 'Hi +Origin (:'
var on = '1'
var Array = new Array('HI","HALLO","HI@","HELLO","SEAS","ZEAS","HUHU","MOIN,"MORGEN","SERVUS","TAG","SERVAS");
function OnEvent_ChatWndReceiveMessage(ChatWnd, Origin, Message, MessageKind){
if (Origin != Messenger.MyName){
Message = Message.toUpperCase()
for(i=0;i<Array.length;i++){
if (Message.substr(0,Array[i].lenght-1) == Array[i]){
ChatWnd.SendMessage('Hi ' + Origin + " (:" );
}
}
}
}
This will make it easier to extend on the script easier and fix any problem that you come accross because it is smaller and easier to read.