Comment 7 for bug 940924

Workaround:

Add this to the bottom of "/usr/share/X11/xkb/symbols/de"

partial alphanumeric_keys
xkb_symbols "qwerty" {
    include "de(basic)"

    name[Group1]="German (qwerty)";

 //key <AB01> { [ y, Y ] };
 //key <AD06> { [ z, Z, zcaron, Zcaron ] };
    key <AD06> { [ y, Y ] };
 key <AB01> { [ z, Z, zcaron, Zcaron ] };
};

Add the new keyboard to:
/usr/share/X11/xkb/rules/evdev.xml
and
/usr/share/X11/xkb/rules/base.xml

After:

 <layout>
      <configItem>
        <name>de</name>

        <shortDescription>de</shortDescription>
        <description>German</description>
        <languageList>
          <iso639Id>ger</iso639Id>
        </languageList>
      </configItem>
      <variantList>
[...]

Add this:

  <variant>
          <configItem>
            <name>qwerty</name>
            <description>German (qwerty)</description>
          </configItem>
        </variant>

Reboot is necessary - since I don't know which services to restart....