A private constructor only allows objects to be constructed from within the class definition. Being an enum, it is easy to get confused, so I usually find it easier to think of an enum as a class with some special features. So when you write:
SLocale.EN_US
Basically, the parameters
Locale.US, "www.abc.com", "www.edc.com", "www.vvv.com", "www.earn.com"
will be passed to the private constructor so that the enum can be instantiated. Enum constructors have to be private.