Success!!
In the file
/usr/share/translations/lipstick-de.qm is the message text hidden between 00 h bytes.
I copied the file to my laptop and edited it with a hex-editor. Very inportant is to use overwrite mode and not insert mode, delete nothing and add nothing, only change the existing letters into the new ones. Start with the new message at the first letter position of the existing message, 31B h. Between the letters is always a 00 h Fill the rest of the letters with 20 h but do not delete anything else!
If the size of the file changes, the system will not accept it and english text appears.
After my first attempt I was happy that I have made a safety copy of the original file!
I typed in my name (to give a little bit more individuality and as a proof of ownership…)
and " - Ladegerät ausgesteckt". ä is E4 h, Komma is 2C h, - is 2D h.
Thanks very much!