Note that US ASCII is 7 bits for 0-127 code points.
Extended ASCII is 8 bits (1 byte) for 0-255 code points.
The extended area is interpreted by loading a different code page depending on the language so that other characters might be displayed.
ISO/IEC 8859-1 is the 8 bit codepage for
ISO/IEC 8859-5 is the 8 bit codepage for
ISO/IEC 8859-9 is the 8 bit codepage for turkish.
Then we get into displaying japanese, korean languages where double-byte encoding is used or Big-5 for chinese.
UTF-8 is variable width, starting with 7 bit US ASCII and has one or more bytes per code point.
UTF-8 eliminates needing to load different codepages for display of character sets between different languages. It reassigns several code points in the upper 128 characters in the first byte to allow for variable-width encoding, using 1 or more bytes for displaying a vastly larger number of characters. Due to it preserving the first seven bits, it is backwards compatible with US ASCII and extensible to cover all language character sets, symbols, punctuation, etc.