How to set up multistore and multilanguage configuration?

[Jens_Noma]

I want to setup up two stores on one installation. Both stores shall be available in English and German.

I want them to be available at the following example urls:

    Store: Engineering (German: Maschinenbau) English Store View: https://www.example.com/engineering/en/ German Store View: https://www.example.com/maschinenbau/de/

    Store: Industry (German: Industrie) English Store View: https://www.example.com/industry/en/ German Store View: https://www.example.com/industie/de/

Via Stores -> Configuration -> General -> Web I selected each of the four store views and entered the aforementioned URLs in the Base URL and Base Link URL input fields.

The problem is: Now the frontend is broken. No matter what url I enter it always returns a 404. The 404 page comes as plain html, no css is applied.

I furthermore have a question: When I enter https://www.example.com it currently redirects me to the first store view https://www.example.com/engineering/en/. What do I have to change if I want to remain on https://www.example.com/ and get a page that lets the customers select between the two stores: Engineering and Industry?