The first page you're greeted with when you visit PlanarAlly will show you a carousel with some of the features of PA as well as a sidebar with a login prompt and an option to register instead.
During registration you can optionally fill in an email address, do note however that it is currently not required for sign-up, which means that there is no solid recovery mechanism in case you lose your password, so make sure you don't lose it ;) that said it is technically possible for the passwords to be changed by a server administrator. That said there is no automated system so your results may vary.
! Any account created is unique to that specific PlanarAlly site and will not exist yet (or even be occupied) on another PlanarAlly site.
In the topleft of the login sidebar there is a icon which when pressed allows you to change the language of the user interface. Note that PlanarAlly is developed in English and, thus, in case a translation of something in the user-interface is missing in the chosen language, the english version of the string will be displayed as a fallback.