Have a gander at PerlUniTut

I suspect your problem is that you need to tell Perl that your input source is Unicode.

eg.

use Encode qw(encode decode);

while ( my $readline = <$fh> ){
   my $foo   = decode('UTF-8', $readline);
}
[download]

etc. I could be way off though...

Update:
Just realised... Unless you actually mean to change the encoding of your data from UTF-8 into something else, you'll need to re-encode it into UTF-8 after you've finished processing it in Perl.

use Encode qw(encode decode);

while ( my $readline = <$fh> ){
    my $foo = decode('UTF-8', $readline);
    #do stuff here 
    $foo = encode('UTF-8', $foo);
    print {$output_fh} $foo;
}
[download]