How to ignore serving certain branches?

How can I build a single URL multilingual site with languages under content, such as:
content/en, content/fr, content/de, etc.
but display only the current language as top level. For example, when in French, public/en and public/de should be ignored and the fr branch displayed as if it were the top level, like DOMAIN/tech/post and not DOMAIN/fr/tech/post

Hugo is a static site generator. There’s nothing in Hugo that addresses your concern. You’d need to either solve that via client-side scripting or with a web server (ie. Nginx).

Solved it.
See: Multilingual Site with two-pass build