As far as I know, the website is in German only. The webmail interface can be switched to any language you want though. I guess you could sign up for it with the help of a German friend or maybe even Google Translate. Since payment is completely anonymous (or paypal), that won't be a problem.

To quote from the FAQ:

  The webmail interface can be switched to other languages. 
  However, the rest of the service is in German, i.e. 
  sign-up, EULA, mail settings (forwarding, POP download, …),
  payment information etc. If you don't know any 
  German, you might miss some things.

  Der Webmailer lässt sich auf andere Sprachen umstellen. 
  Allerdings ist unser Angebot ansonsten komplett 
  deutschsprachig, also Anmeldung, AGBs, Einstellungen rund 
  um die Mailadresse (Weiterleitungen, POP-Sammeldienst,…), 
  Zahlungshinweise usw. Wer gar kein Deutsch kann, geht da 
  vielleicht etwas verloren.