I'm using Data::Dumper because I have a complex XML structure which I need to have in a human readable format.

Data::Dumper is really more of a debugging aid than a pretty-printer. You could try out some other modules, such as Data::Printer. See also Data::Dumper with unicode for a question quite similar to yours.

use open qw/ :std :utf8 /;
use Data::Printer;
my $str = "Nach R\x{fc}cksprache mit";
p $str;
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Next time, please provide all the information that you have split into multiple posts in this thread into a single post. I know what I mean. Why don't you?