With some no-ops removed.

#@a = split //, 
# 'Juste re ha .eht'.
# 'r P  kc l  rona ';

@a = ('J','u','s','t','e',' ','r','e',' ','h','a',' ','.','e','h','t',
+'r',' ','P',' ',' ','k','c',' ','l',' ',' ','r','o','n','a',' ');

for($n=1;$i<4;){
#    y/if/f/ unless@a;
    do {
        @a=reverse @a;
        sleep $n
    } if fork;
    splice @a, @a/2;
    $n*=2;
    #goto P;
# P:
    print shift @a;
    $i++
}

#goto P if
#truncate STDERR,
#fileno STDERR%
#ord STDERR;
[download]

The actual printing is done by reversing the array (in the parent process only), cutting off the last half, and then printing a character. The sleep $n gets the order of the output all right. I'll be honest, I barely understand it :). ++, well done. For what it's worth, here's the array commented with the order (sorry for the long lines, it makes more sense when you unwrap them):

@a = ('J','u','s','t','e',' ','r','e',' ','h','a',' ','.','e','h','t',
+'r',' ','P',' ',' ','k','c',' ','l',' ',' ','r','o','n','a',' ');
#      1   1   1   1   8  12   5   5       7   7  14  10   3   3   3  
+ 4   4   4  11  15   8   8       6   6  13   9   2   2   2   2
#@a = qw/1 1 1 1 8 12 5 5 n 7 7 14 10 3 3 3 4 4 4 11 15 8 8 n 6 6 13 9
+ 2 2 2 2/;
[download]