You could transliterate into ASCII in a second step, e.g. using Text::Unidecode:

#!/usr/bin/perl

use strict;
use warnings;
use MIME::Words qw(:all);
use Text::Unidecode;

my @encoded = (
    '=?iso-8859-1?Q?Communiqu=E9?=', '=?iso-8859-1?Q?Telef=F3nica?=',
    '=?ISO-8859-1?Q?Montre=E1l?=',   '=?iso-8859-1?Q?Minist=E8re?=',
);
for (@encoded) {
    my $s = decode_mimewords($_);
    print unidecode($s), "\n";
}

__END__
Communique
Telefonica
Montreal
Ministere
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