It looks like the meat of your question could be answered thus:

use warnings;
use strict;

my @deleted = ('Entry 1', 'Entry 2', 'Entry 3');
my $str = "Deleted forum";
@deleted > 1 ? ($str .= 's: ') : ($str .= ': ');
$str .= join ', ', @deleted;
print $str;
[download]

Prints:

Deleted forums: Entry 1, Entry 2, Entry 3
[download]