Ascii is 7 bits. What people think of as 8-bit ASCII is actually code page 437, the alternate characters added to the PC BIOS in the original IBM PC. Like UTF-8 it uses the most significant bit in a 1 byte ASCII char to determine if it should use a character from ASCII if 0 or the extended 437 characters which includes ü if 1. https://en.wikipedia.org/wiki/Code_page_437