add internationalization to event form

issue: translation (internationalization) is only implemented on homepage yet. Internationalization is not implemented on event form yet.

goal: implement internationalization (english / german translation) to event form based on initialization already implemented on homepage

https://stempelheft.multimediatechnology.at/events/new -> implement I18n in files: new.html.erb & _form.html -> update en.yml and de.yml -> adjust unit tests and system test if needed

BEFORE: (based on internationalization initialization)

german version contains english:

english version contains german:

internationalization of homepage is already implemented on staging

After

english:

german: