Thanks for your replies and the inspirations. I realized it now the following way:

I created a variable “$Anzahl-Offen” for counting the open windows . This variable is increased when a window sensor is opened and decreased when it’s closed. When a certain window is opened I set a corresponding text variable with the name of the sensor like “Window in the bathroom”. The text variable is set to an empty string when the contact is closed. When the front door is opened I check the number of open windows and if it’s greater than 0 I play a text message on the Google Home which includes the text variables from 2. If a window is closed, the corresponding variable is empty and therefore this produces no output. For usability I have two rules. One for one open window and another one, when more than one window is open. When kontakt-haustur is opened and if "$Anzahl-Offen" equals "1" then play text "Achtung, offen ist: $wc-ofen-text, $bad-ofen-text, $terasse-ofen-text" vol $cc-volumen on CC-Diele When kontakt-haustur is opened and if "$Anzahl-Offen" is greater than 1 play text "Achtung, offen sind: $wc-ofen-text, $bad-ofen-text, $terrasse-ofen-text" vol $cc-volumen on CC-Diele

For each new sensor I “just” need to add 2 rules which makes it manageable for me. Furthermore I don’t need an external script.

Edit / Rename option for rules and devices IDs