Instead, create locale with codecvt_utf8 facet on all platforms (even if
codecvt_utf8 is deprecated since C++17). There is no guarantee that
"en_US.UTF-8" is a supported locale name, so the locale constructor might throw
a runtime_error. (See the discussion in the comments to
https://gerrit.libreoffice.org/#/c/62508/ "Add check for en_US.utf8 locale"
for a real-live example of issues caused by that.)
(And the and headers apparently need to be included always,
regardless of NUMBERTEXT_BOOST.)
Instead, create locale with codecvt_utf8 facet on all platforms (even if codecvt_utf8 is deprecated since C++17). There is no guarantee that "en_US.UTF-8" is a supported locale name, so the locale constructor might throw a runtime_error. (See the discussion in the comments to https://gerrit.libreoffice.org/#/c/62508/ "Add check for en_US.utf8 locale" for a real-live example of issues caused by that.)
(And the and headers apparently need to be included always,
regardless of NUMBERTEXT_BOOST.)