Menu issues

Hello! Can you help me with the menu and the OnePress theme? I changed the names in the menus that I needed and left the links in order to scroll through the homepage. However, when on the last page ‘Sprachen’ in the menu and selecting some of the languages (which I made as posts), transfer me to that selected page, then that menu does not work, so when I click on any section in the menu, he transferred me the complete look of the site to the original, How can I save it, stay as I set it, that the whole site works with my menu, and it remains in the way I did it? Save me please and help 🙂 Thanks!

The page I need help with: [log in to see the link]