Headless mode/ElementAPI: how to set the frontend's baseUrl in the backend endpoint?
Apparently, the answers are the following:


Redactor doesn't know how to output slugs/URIs instead of full URLs
Possibly a solution comes up with craft in the future
My API setup is suboptimal: In fact, I did set the baseUrl including the language: https://frontend.com/de. The recommendation is to not do that at the moment but keep one "Site" for all endpoints in all languages. This can be added as another, separate site in craft! So we'd have 3 language sites in craft and a separate site for the endpoint. The language is then part of the endpoint's data. And the endpoint's URL is https://endpoint.site/api/de/foo instead of https://backend.site/de/api/foo. Yes, I guess that makes sense! Thanks again, Oli!