javafx accessibility - how to read text (with OS narrator) on window shown?

I want to tell the narrator to read the window description when it's shown.

For example:

• This is the log-in window;
• This is the main system window. Press XXX for the menu.
• An error has occurred: The error is...

We have some low vision users and even blind users using the system.

The narrator is working for buttons and fields, but I did not find a way for it to work on window shown.

How to do it?

Edit 1:
One way to do it is to requestFocus() a label with setAccessibleText().
One thing I could not figure out is how to read Alert dialogs.