The only rule is that your comments are roughly on topic. So no advertising and that kind of thing. I would prefer to nurture creativity than be too strict, so it'll stay fairly open for the moment (at least while there are still design choices to be made).
Please feel free to share your thoughts in German if it is your native language (I know there are quite a few German speaking supporters)! Silas will be acting as the community manager for German members and will help relay messages.
Talking history is still definitely on topic, especially if it is relevant to the game:)
Thanks for your ideas and feedback!