[Feature Request] Web UI language switcher

[thkrmr]

Web UI currently defaults to picking the language of the interface based on what the browser reports / what the HTTP headers are (presumably). Offer an option to be able to pick between auto/en/de per user as a setting, or at least allow to pick the interface language per web session.

While auto detection is sensible, offering an override to the user is logical, too. I might want to use the interface in English or German, depending on my needs, I shouldn't have to fiddle with changing my system settings or the settings of my browser. As most pages on the internet do which serve content in multiple languages.

By the way, the PDF export is always in German, regardless of the UI language.