So if I understand correctly the first datefield to get localized date names would trigger AJAX call to the server and then the result would be cached to client side if there are more datefields in the page?
Either that approach or then supply the names as parameters in DateField.java
This would add the size of the original response, but would save one round trip to server. (Which approach is more efficient depends on the number of datefields in the page)
I would like to see the no-server-round-trip approach, as usually there are max 2 datefields in one page.