Using curses_unicode.patch:

 - without ncursesw: addch('é') raises an OverflowError because 'é'.encode('UTF-8') is 2 bytes and not 1 byte
 - with ncursesw: the charset is displayable character depends on the locale encoding (e.g. € cannot be printed with ISO-8859-1 locale encoding)
 - with ncursesw: any character can be printed with a UTF-8 locale encoding (including non-BMP characters: U-10000..U+10FFFF)

It would be possible to support multibyte encoded character (like é in UTF-8) for addch() by calling addch() multiple times, one per byte, but I would prefer to keep _curses simple and not workaround libncurses limitations (bugs).