Nope, there's only one global locale, it's not per-thread. If it's per-thread, you can do

std::locale::tss_global(std::locale("koi8-r")); // do some work with program_options std::locale::tss_global(std::locale(""));

I do this all the time (but using a scope guard), for globals I've declared thread-local. This essentially simulates dynamic scoping (which I'd prefer to see supported directly by the language, as an alternative to lexical scoping). Perhaps a Boost library for dynamically scoped properties would be nice? -Jonathan