Improve registration handling (i18n, login link)

[StefanSchubert]

Is your feature request related to a problem? Please describe.
During email registration workflow, the user gots an email which isn't i18n aware. (Because it's send by the backend, not the frontend). In addition the user has no link in the mail to the login form.

Describe the solution you'd like
As new user, who is not capable of english (fallback language), I want to read the email verification notice in the same language I hat in the UI during registration process. There for, when the frontend registers a new user against the backend, the browsers language setting needs to be transmitted as well and stored along with the registration token,
or if the user profile has already the expected language stored, then the email sends by the server just needs to read it for building up an i19n answer.