** International character set support (MULE)
Emacs now supports a wide variety of international character sets,
including European variants of the Latin alphabet, as well as Chinese,
Devanagari (Hindi and Marathi), Ethiopian, Greek, IPA, Japanese,
Korean, Lao, Russian, Thai, Tibetan, and Vietnamese scripts. These
features have been merged from the modified version of Emacs known as
MULE (for "MULti-lingual Enhancement to GNU Emacs")
Users of these scripts have established many more-or-less standard coding systems for storing files. Emacs uses a single multibyte character encoding within Emacs buffers; it can translate from a wide variety of coding systems when reading a file and can translate back into any of these coding systems when saving a file.
Keyboards, even in the countries where these character sets are used, generally don't have keys for all the characters in them. So Emacs supports various "input methods", typically one for each script or language, to make it possible to type them.
The Emacs internal multibyte encoding represents a non-ASCII character as a sequence of bytes in the range 0200 through 0377.
The new prefix key C-x RET is used for commands that pertain to multibyte characters, coding systems, and input methods.
You can disable multibyte character support as follows:
(setq-default enable-multibyte-characters nil)
Calling the function standard-display-european turns off multibyte characters, unless you specify a non-nil value for the second argument, AUTO. This provides compatibility for people who are already using standard-display-european to continue using unibyte characters for their work until they want to change.