REPOSITORY ARCHIVED nowide is part of boost now: https://github.com/boostorg/nowide
There is also a standalone version (branch and releases) and it works with c++11.
A clone of http://cppcms.com/files/nowide/ (see documentation).
From the documentation:
Boost.Nowide is a library implemented by Artyom Beilis that make cross platform Unicode aware programming easier.
The library provides an implementation of standard C and C++ library functions, such that their inputs are UTF-8 aware on Windows without requiring to use Wide API.
Copyright (c) 2012 Artyom Beilis (Tonkikh)
Distributed under the Boost Software License, Version 1.0.