> implicit declaration of function ‘wget_wch’

Oh oh, I expected such error: it means that your ncurses library don't have the wide character API. The compiler command confirm that: "gcc ... -lncurses ...". You use libncurses and not libncursesw.

Antoine told me that libncursesw is available on its OS, but Python chose libncurses. I suppose that it's because readline is linked to libncurses (and not libncursesw) => see issue #7384.

Antoine setup is not rare: many Linux distro link readline to libncurses, and so Python cannot use libncursesw.

For this issue, it's not a problem: we can just add a test to check if get_wch is available or not, and only define the Python function if the C function does exist. But for #12567, it's a bigger problem because it means that we cannot always use the wide character functions if the argument is Unicode (character/string).