There is a header (" < locale > ") in Standard ISO C++.
Is there any good references for Internationalization and localization in ISO C++?
The best sources I know are:
Standard C++ IOStreams and Locales by Langer and Kraft (it has a tutorial part and a more reference part)
the appendix in some version of the third edition of The C++ Programming Language by Stroustrup (which is also available online) is more a user guide than a reference
the relevant section in the standard is only a reference and not suitable as a user guide.