If the number of trigger words is limited, you could use a text file for each word, with each reply on a single line and use $read. Type /help $read and look at the first example for $read.

Also remember that the trigger you gave only responds to "Hi", not to "Hi DfD" or whatever.

A last point: with the current script, you will be kickbanned on some channels, so make sure you have permission from the channel operators (or are one yourself), and limit it to only those channels.

Code:
on 1:TEXT:Hi:#chan1,#chat:{
  msg # $read(hi.txt)
}


hi.txt:
Hi there $nick
What's up $nick $+ ?