When you want to remove or replace an existing configuration element, you need to refer to it by its English name. You cannot refer to it by its localized name.

Now, how to learn what is the English name of a given configuration element? The obvious solution is to look in the bundled configuration files:

Given the fact that the names of configuration elements are often displayed by the GUI of XXE (the name of document templates are listed in the File → New dialog box, the names of CSS style sheets are listed in the View menu, etc), a simpler solution consists in temporarily switching to the English locale. In order to do this, use Options → Preferences, General section, Locale combobox. More information in Locale in XMLmind XML Editor - Online Help.