Sorry, Sue - the problem seems to be different:
In the EE 1.7. I used the Email-notification “User Comment Notification” - with this a user was informed about follow-up comments. (I at least assume so, don’t have a 1.7 at hand, but it was migrated automatically to 2.1/2.2).
Now in EE 2.2 the user is informed with the “User Comments Added Notification”. The “User Comment Notification” has the right content (my German blabla).
So my original template is not in use, but the default one.
I now copied my custom-content into the Added-Notification-template. Actually this does work.
I don’t understand the difference between the function of the two templates, the documentation is a little “thin” about this (docs:// message pages)
For me now everything is ok, but I assume a lot of people upgrading from 1.7 -> 2.1/2.2 do have this problem without recognizing it (because normally as admin you don’t get notifications of follow-up comments). For them this thread was made. Amen.
And thank you, Sue, for being willing to help me!
(and my case closed)