use strict;
use warnings;

my @word = qw(
    constituci\xf3n contribuci\xf3n destituci\xf3n devoluci\xf3n disminuci\xf3n
    constituciones contribuciones destituciones devoluciones disminuciones
    foo
);

my $vowels     = 'aeiou\xe1\xe9\xed\xf3\xfa\xfc';
my $consonants = 'bcdfghjklmn\xf1pqrstvwxyz';

my $revowel      = qr/[$vowels]/;
my $reconsonants = qr/[$consonants]/;
my $R2;
my $suffix;

for my $word (@word) {
    ($R2) = $word =~ /^.*?$revowel$reconsonants.*?$revowel$reconsonants(.*)$/;
    $R2 ||= '';
    if ( ($suffix) = $R2 =~ /(uciones|uci\xf3n)$/ ) {
        # uci\xf3n uciones
        # replace with u if in R2
        $word =~ s/$suffix$/u/;
        print "Step 1 case 4: $word\n";
    }
}