188.8.131.52 "fixed" the problem in 2.0.5 by simply reverting the relevant code to the way it was pre-2.0.5. So it sounds like everything is working as expected.
The issue is that, from Java, it is difficult, and likely error prone, to detect the user's keyboard layout and adjust the default keyboard shortcuts appropriately. I don't believe it's as simple as using the default Locale (although that may be sufficient in many cases), as an application's locale can be toggled separately from the system locale and keyboard layout. I could be wrong of course, and I'm open to ideas. But I'll only implement something if it's foolproof.
FWIW, you can install this shortcut for your QWERTZ users if you want as follows (untested):
InputMap im = textArea.getInputMap();
// Old shortcut doesn't hurt, but might as well remove it.
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_SLASH, InputEvent.SHIFT_MASK|InputEvent.CTRL_MASK), RSyntaxTextAreaEditorKit.rstaToggleCommentAction);