Some questions.

1. Active Perl or Strawberry Perl ?

2. What shows your $_ in your program ? With my XP, it shows 8.3 style file names(For example, "Program Files"=> Progra~1).

foreach (@files) {
  print "$_\n";
  my $original = $_;
  s/canción/poesía/;
  rename "$directory\\$original", "$directory\\$_";
}
[download]

What would $_ with Windows 7?.

3. When you install Win32::Unicode,Win32::Unicode::Dir, Does this work ?

use strict;
use warnings;
use utf8;

use Win32::Unicode;
use Win32::Unicode::Dir;

my $wdir = Win32::Unicode::Dir->new;
$wdir->open('./');

while ( my $file=$wdir->fetch ) {
    next if( $file !~ /^canción/ );
    my $file_new=$file;
    $file_new =~ s/canción/poesía/;

    printW "$file ==> $file_new\n";
    #moveW($file, $file_new) or die $!;
}
$wdir->close;
[download]

I tried with ActivePerl. As "andalou" says, I also met the same error when calling moveW. It seems lacking XS's function which is calling Win32API. I guess Strawberry Perl works ... fine?

Update:
I understand OP="andalou" now. If you are using Active Perl,

ppm install "http://sourceforge.jp/frs/g_redir.php?m=jaist&f=%2Fassp%2
+FASSP+V2+multithreading%2Fpackages%2FWin32-Unicode.ppd"
[download]

will remove your Win32::Unicode error messages. </code>