Comment 2 for bug 1666314

Just came across this recent message on one of GCC's mailing lists (no replies yet):
https://gcc.gnu.org/ml/gcc-help/2017-02/msg00080.html

Similarly, there is a known issue with libstdc++ on (older) versions of Mac OS X (before the switch to clang and libc++ as default): C++ locale only supports C, POSIX
https://mail.gnome.org/archives/gtkmm-list/2010-April/msg00030.html