I try to use some Boost.Locale functions and I get an std::bad_cast exception thrown?

Answer: You probably try to use incorrect std::locale object. All Boost.Locale tools relay on std::locale object's facets. The locale object should be generated with generator class and then passed to the function or alternatively global locale should be set using std::locale::global() function such that global locale (and default created one) would have required facets to use.

I had installed global locale and try to write something to stream but still get wrong output? For example:

    #include <boost/locale.hpp>
    #include <iostream>
    int main()
    {
        boost::locale::generator gen;
        std::locale::global(gen(""));
        std::cout << boost::locale::as::date << std::time(0) << std::endl;
    }

Prints a number instead of a date.
Answer: You forget to imbue the locale to the stream. Changing the global locale does not affect the locale in existing iostream objects. Thus because std::out and other global streams were created before changing the global locale Boost.Locale manipulators have no effect. You need to write:

    #include <boost/locale.hpp>
    #include <iostream>
    int main()
    {
        boost::locale::generator gen;
        std::locale l = gen("");
        std::locale::global(l);
        std::cout.imbue(l);
        std::cout << boost::locale::as::date << std::time(0) << std::endl;
    }