Long story abbreviated, I have been at it for hours but now I have to give up and ask the master of templates, scss and everything.
I would like to change the look of a single submenu (language switcher, as you recommended for the UX). As far as I have found out I can do that in my custom.scss changing the css for the g-menu-item-container class. It is easy to change the look of a single top menu item or all of the the submenus. My problem is that I do not find a unique identifier for the submenu container I want to change. There is a class g-menu-item-language-page-de---module-hOLDc but the last part of this class changes dynamically. Any help would be very welcome.