The second documentation you linked tells you how to do it. First you open your profile on the bottom left and switch Zammad to the language you want to translate your string to. Then you either go to the admin backend and open the Translations section, search for your overview name and change the translation, or the easier way would be to just open the overviews and then press CTRL+SHIFT+T to switch to the inline translation mode. Every string that is encased in a red dotted line can be translated on the fly. Just change what you want and leave inline translation mode with CTRL+SHIFT+T again.