Hi Benedetta,

Thank you for bringing this to our notice. As a token of gratitude, I am updating your Telerik points. 

Please subscribe to this issue created in the Issue tracker of the Kendo UI for Angular to receive future updates pertaining to the same.

As a workaround, please add the following snippet in the openWindow() function to change the closeTitle and the maximizeTitle of the Kendo UI WindowService:

setTimeout(() => {
  var closeTitle = document.querySelectorAll(".k-window-actions .k-button[kendowindowcloseaction]");
  closeTitle[0]["title"] = "TEST";

  var maximizeTitle = document.querySelectorAll(".k-window-actions .k-button[kendowindowmaximizeaction]");
  maximizeTitle[0]["title"] = "TEST";
});

In this StackBlitz example, I have changed the close button and the maximize button title of the Kendo UI Window.

Please let me know if I can further assist you.

Regards,
Hetali
Progress Telerik