Here's a way to reverse a Unicode string using the regular expression character class \X to match Unicode extended grapheme clusters:

my $edocinU = join '', reverse $Unicode =~ m/\X/g;
[download]

Here's a demonstration using Vietnamese (tiếng Việt) words:

#!perl

use strict;
use warnings;
use utf8;

binmode STDOUT, ':encoding(UTF-8)';

my $Moonshine = "Rượu đế";
my $enihsnooM = join '', reverse $Moonshine =~ m/\X/g;

print "$Moonshine\n";
print "$enihsnooM\n";

__END__
Rượu đế
ếđ uợưR

LATIN CAPITAL LETTER R
LATIN SMALL LETTER U
COMBINING HORN
LATIN SMALL LETTER O
COMBINING HORN
COMBINING DOT BELOW
LATIN SMALL LETTER U
SPACE
LATIN SMALL LETTER D WITH STROKE
LATIN SMALL LETTER E
COMBINING CIRCUMFLEX ACCENT
COMBINING ACUTE ACCENT

[I was forced to use <pre> tags instead of <code> tags here to display the actual Vietnamese characters rather than their HTML character entities.]