Hi Joerg,
I can help out here.
I have this snippet to remove “You will receive the tickets in a seperte email.”
https://gist.github.com/jesseeproductions/ec0756a728a65dec0266
Just remove New Text Here and it will no longer display in the email.
Ticket Email
To customize the ticket email please follow our themer’s guide:
https://theeventscalendar.com/knowledgebase/themers-guide/
To move and edit this file in your theme:
wp-content\plugins\the-events-calendar\views\tickets\email.php
Order Email
“Payment Method:” is in the WooCommerce Order email that is done in WooCommerce and I do not have information on how to translate that. It is either in their po file for the plugin or they may have coding translate it directly.
Let me know if you have any follow up questions.
Thanks