https://gcc.gnu.org/bugzilla/show_bug.cgi?id=5499
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- numpunct<char>::_M_initialize_numpunct in config/locale/gnu/numeric_members.cc says: // NB: There is no way to extract this info from posix locales. // _M_truename = __nl_langinfo_l(YESSTR, __cloc); _M_data->_M_truename = "true"; _M_data->_M_truename_size = 4; // _M_falsename = __nl_langinfo_l(NOSTR, __cloc); _M_data->_M_falsename = "false"; _M_data->_M_falsename_size = 5; I don't know where the C++ standard expected this information to come from.