Language selection should be a well-known shortcode
In Frab and pretalx, languages get "de" or "en" assigned according to their language. The hub currently uses a simple text field for the language, resulting in a (not) nice mixture of "de", "en", "English", "German", "Deutsch" etc in the generated Fahrplan.
The hub should normalize the language selection to the shortcodes used by Frab/pretalx so people don't get confused by the mixture of locale definitions.