The REST API reports "he" locales as "iw"

So, if we add "he" to the list of accepted locales, this gets translated into "iw" at run-time in JSON responses.

This is reported against core because the fix needs to be applied to the default messageConverters which are registered in core.

For legacy reasons, the toString() method in Java's Locale class returns "iw" when the locale is "he" (or any derivative). Because, by default Jackson serialises Locale}}s by calling {{toString(), this results in our REST API reporting different values from what is in the interface.

This is fixed in Jackson 3.0, but that isn't released yet, so we need a workaround.