You could use regex in the trigger to make it shorter:

On $*:TEXT:/^[~]*/Si:*: { 
  if ($mid($1,1) == ~do) {
    $antiflood($1) 
    $iif($query($nick),describe $2 $3-,describe # $2-)
  }
  Elseif ($mid($1,1) == ~say) {
    $antiflood($1)
    $iif($query($nick),msg $2 $+(% ,$3-),msg # $+(''',$2-,'''))
  }
}