hi, from the documentation [1] : "[...] the library uses the codecvt<wchar_t, char> locale facet from the global locale." The quote is taken from the unicode-documentation part. May i ask why the locale is taken from the global locale, instead of the locale assigned to the stream? What I'd like to do is (currently yields a logic_error) // assume stream contains "a = 1,2" // ... std::locale loc("German_Germany"); stream.imbue(loc); po::parse_config_file(stream, opts, false); instead i have to std::locale loc("German_Germany"); std::locale::global(loc); po::parse_config_file(stream, opts, false); to parse the config file correctly. Best regards, Christoph [1] "http://www.boost.org/doc/libs/1_43_0/doc/html/program_options/howto.html#id1...