<?xml version="1.0" encoding="UTF-8"?>
    <tweets>
        <tweet>
            <content>hola, bonita </content>
        </tweet>
        <tweet>
           <content>hola, dictadura </content>
        </tweet>
   </tweets>

my %hashcorpus = (
        dictadura    => "nombre",
        bonita   => "adjetivo", );

#!/usr/bin/perl
    use warnings;
    use strict;
    use utf8;
    use XML::LibXML;

    my $filename = 'corpus.xml';
    my $dom = XML::LibXML->load_xml(location => $filename);
    foreach my $tweet ($tom->findnodes('//tweet'))
    {
       my @content = $tweet->findnodes('./content');
       die "<tweet> didn't have exactly one <content>: $tweet"
       unless @content==1;

       my $content = $content[0]->textContent;

       foreach my $key (keys %hash)
       {
         my $content =~ s/ $key / $hashcorpus{$key} /g;
       }

       $content[0]->removeChildNodes();
       $content[0]->appendText($content);
       #~ #say $content;

    }

    print $tom->toString;