Current state

Alpha

The game is currently in Alpha state according to the developer. Sign-up for joining alpha-testing is available through the official Pax Dei website and may involve an NDA.

The first wave of Alpha testers will be invited "before too long™" and will start in a region of Gallia.
Here isare athe quotetwo most current quotes from the developer which gives a more detailed answer to the current state of the game:

We are coming up to a stage where we think we can offer a large number of Alpha testers an enjoyable stay in a relatively stable client, with enough to do to start feeling at home in the world of Pax Dei. But obviously there are a lot of things yet to be implemented and a huge amount of content that needs to be produced for a full and proper launch.

We have been doing smaller play tests for a long time now, only by invite and under NDA and we will be expanding on that in the coming weeks and months. I cannot say right now when we let people in by the thousands, I would not be doing anyone a favour, but we want people into the alpha client as soon as we can be relatively sure they are not going to be frustrated by server and/or game performance.

...

Some further clarification was added recently, here's another quote:game/testing:

We’re still a few months away from a large-scale Alpha test. Rest assured that when we’re ready to announce it, we’ll publish official communication with all details.

We are running regular, small playtests under NDA with our friends and family to test parts of the game we intend to have available for larger-scale testing. One should start pretty soon, actually. We’re sorry we can't add you to these playtests, but they will primarily be used to test specific features and setups in preparation for the Alpha which we can invite you to.