Effects: Calls each registered callback pair (fn,index) ([ios.base.callback]) as (*fn)(imbue_event,*this,index) at such a time that a call to ios_base::getloc() from within fn returns the new locale value loc.
Returns: The previous value of getloc().
Postcondition: loc == getloc().
Returns: If no locale has been imbued, a copy of the global C++ locale, locale(), in effect at the time of construction. Otherwise, returns the imbued locale, to be used to perform locale-dependent input and output operations.