my $str = '\u00E1\u015F';
$str =~ s/\\u([0-9a-fA-F]{4,6})/chr(hex($1))/eg;
open my $handle, '>:encoding(UTF-8)', $file
    or die "Can't open file `$file' for writing: $!";
print $handle $str;
close $handle or warn $!;