For many but not all pages there is a German and an English version. The server will automatically detect which language preferences you have set in your browser and send you the right version. You can switch versions temporarily by clicking on the flag icon.
The layout was developed for modern browsers which support cascading style sheets (CSS). Even so you can use old and text-mode browsers to see and do everything but it might not look that well everywhere.
For GUUG staff (and in the near future also for GUUG members) there are accounts that allow access to some special information and options. Please ask firstname.lastname@example.org if you need an account.
The login only works properly if you have enabled cookies in your browser. The cookie will be deleted once your browser session is closed. You don't need cookies for normal site operation.