I have a game which uses std::wstring as its basic string type in thousand of places as well as doing operations with wchar_t and its functions: wcsicmp() wcslen() vsprintf(
Qt provides an excellent copy-on-write, international-friendly string implementation, QString, that is LGPLed.
You could, in theory extract it from the Qt source and use it in your own project. You will find the QString implementation in src/corelib/tools/qstring.h and .cpp in a Qt source download. You would also need the QChar, QByteArray, QAtomic, and QNamespace includes/classes (all under the corelib folder,) and you should define QT_NO_STL_WCHAR when compiling. (For this I would compile by hand or using my own script/Makefile.) Not simple, but once you get it up and running your life will be a lot simpler. It's better than reinventing the wheel, because it comes with loads of convenience functions and features.
Rather than stripping out just QString, you could also just use the QtCore module as a whole. See the android-lighthouse project for a Qt port to Android. (Also, it might be better to get your sources from there than from the above "vanilla" link, regardless of what you do.)