--- Comment #20 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Compiler support for char16_t and char32_t has been complete for many years.
The libstdc++ support required by the standard has been complete since GCC 5.1,
but I don't know if Paolo had more in mind (we don't implement all locale
facets for char16_t and char32_t, which means e.g.
std::basic_stringstream<char16_t> doesn't work, but the standard doesn't
require it to work).