I have just confirmed the above situation (default locale is GB) and get the results below when printing the date with the following code:
Date dt = new Date();
String myString = DateFormat.getDateInstance().format(dt);
System.out.printf("It is now: %s\n", myString);
C:\Users\rjmac\Documents\VSCode\Java>java test
It is now: 26 May 2021
Java test result: 0
C:\Users\rjmac\Documents\VSCode\Java>java -D"user.country=US" test
It is now: May 26, 2021
Java test result: 0