The output of Data::Dumper will always show Nach R\x{fc}cksprache mit because Data::Dumper tries to restrict its output to 7-bit ASCII, at least with some options.

If you want something else, please show a SSCCESCCEE, because I don't really understand what you're asking for and it's most easy to demonstrate in ten lines of code.

use strict;
use Lyo::OSLC::CQ::CM;
use Data::Dumper;
use Encode qw(encode decode);

...

my $client = Lyo::OSLC::CQ::CM->new;

...

my $data    = $client->oslcWhere(...); # get data from ClearQuest
my $xml     = Dumper($data);
my $xml_out = encode('UTF-8', $xml);
print $xml_out;
[download]

I am wondering why you are using Dumper() and encode() at all? What happens when you do the following?

use open qw/:std :utf8/;
use strict;
use Lyo::OSLC::CQ::CM;
...
my $client = Lyo::OSLC::CQ::CM->new;
...
my $data = $client->oslcWhere(...);
print $data;
[download]

The documentation of the ->oslcWhere() method of the module Lyo::OSLC::CQ::CM (which does not appear to be on CPAN; so I hope I've found the right one via googling) says:

The response from the server is returned in XML format.

So in that case I would use an XML parser such as XML::LibXML to parse it.

Why do you have a string named $xml which is assigned the output of Data::Dumper?

Note that, as I already said, Data::Dumper likely doesn't output characters above 127 but instead outputs Perl code that's roughly equivalent.

You most likely want to construct your strings differently.

What is the actual content of $data?

Maybe you want to re-read SSCCE (which I misspelled earlier, sorry) to give us some more concrete code, data and output to work with.