You could store the message definitions in an (external) xml configuration file.

use strict;
use XML::Simple;

my $msg = LoadMsgConfig();
print "$msg->{0}\n";      # look up by id
print "$msg->{thanks}\n"; # look up by mnemonics

sub LoadMsgConfig
{
    my $xs = new XML::Simple();
    my $xmlmsg = do { local $/; <DATA> };
    my $tags = $xs->XMLin($xmlmsg);

    return undef if ! defined $tags->{msg};

    my %msg;
    foreach (keys %{$tags->{msg}})
    {
        $msg{$_} = $tags->{msg}{$_}{text};
        $msg{$tags->{msg}{$_}{id}} = $msg{$_};
    }

    # undef $xmlmsg, $tags, $xs;
    return \%msg;
}

__DATA__
<?xml version="1.0"?>
<config>
  <msg id="0" name="wrong_input"  text="Wrong input"/>
  <msg id="1" name="thanks"       text="Thanks for signing up with us"
+/>
  <msg id="2" name="go_away"      text="Go away hacker"/>
</config>
[download]

And the output -

Wrong input
Thanks for signing up with us
[download]