Fixed email templates

The last update of our shop software broke the email templates.
Sorry that we didn’t notice this earlier.
This manifested in automatic emails e.g. about an order being shipped to be mostly empty.

Except for one thing, they should all work again and we also clarified the wording in many places.
The missing fix is that the label for a new status of the order is currently displayed in German even for English customers. This was fixed a long time ago but the way it was fixed (a specific function call in an email template) is no longer allowed (no more function calls. Only variable access.).

We did raise an issue in the GitHub repository of the shop software pointing out this regression bug and why it came up again.