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27.3 Language Environments
All supported character sets are supported in Emacs buffers whenever
multibyte characters are enabled; there is no need to select a
particular language in order to display its characters in an Emacs
buffer. However, it is important to select a language environment
in order to set various defaults. The language environment really
represents a choice of preferred script (more or less) rather than a
choice of language.
The language environment controls which coding systems to recognize
when reading text (see Recognize Coding). This applies to files,
incoming mail, netnews, and any other text you read into Emacs. It may
also specify the default coding system to use when you create a file.
Each language environment also specifies a default input method.
To select a language environment, you can customize the variable
current-language-environment or use the command M-x
set-language-environment. It makes no difference which buffer is
current when you use this command, because the effects apply globally to
the Emacs session. The supported language environments include:
Belarusian, Brazilian Portuguese, Bulgarian, Chinese-BIG5,
Chinese-CNS, Chinese-EUC-TW, Chinese-GB, Croatian, Cyrillic-ALT,
Cyrillic-ISO, Cyrillic-KOI8, Czech, Devanagari, Dutch, English,
Ethiopic, French, Georgian, German, Greek, Hebrew, IPA, Italian,
Japanese, Kannada, Korean, Lao, Latin-1, Latin-2, Latin-3,
Latin-4, Latin-5, Latin-6, Latin-7, Latin-8 (Celtic),
Latin-9 (updated Latin-1 with the Euro sign), Latvian,
Lithuanian, Malayalam, Polish, Romanian, Russian, Slovak,
Slovenian, Spanish, Swedish, Tajik, Tamil, Thai, Tibetan,
Turkish, UTF-8 (for a setup which prefers Unicode characters and
files encoded in UTF-8), Ukrainian, Vietnamese, Welsh, and
Windows-1255 (for a setup which prefers Cyrillic characters and
files encoded in Windows-1255).
To display the script(s) used by your language environment on a
graphical display, you need to have a suitable font. If some of the
characters appear as empty boxes, you should install the GNU Intlfonts
package, which includes fonts for most supported scripts.1
See Fontsets, for more details about setting up your fonts.
Some operating systems let you specify the character-set locale you
are using by setting the locale environment variables LC_ALL,
LC_CTYPE, or LANG.2 During startup, Emacs looks up your character-set locale's
name in the system locale alias table, matches its canonical name
against entries in the value of the variables
locale-charset-language-names and locale-language-names,
and selects the corresponding language environment if a match is found.
(The former variable overrides the latter.) It also adjusts the display
table and terminal coding system, the locale coding system, the
preferred coding system as needed for the locale, and—last but not
least—the way Emacs decodes non-ASCII characters sent by your keyboard.
If you modify the LC_ALL, LC_CTYPE, or LANG
environment variables while running Emacs, you may want to invoke the
set-locale-environment function afterwards to readjust the
language environment from the new locale.
The set-locale-environment function normally uses the preferred
coding system established by the language environment to decode system
messages. But if your locale matches an entry in the variable
locale-preferred-coding-systems, Emacs uses the corresponding
coding system instead. For example, if the locale ‘ja_JP.PCK’
matches japanese-shift-jis in
locale-preferred-coding-systems, Emacs uses that encoding even
though it might normally use japanese-iso-8bit.
You can override the language environment chosen at startup with
explicit use of the command set-language-environment, or with
customization of current-language-environment in your init
file.
To display information about the effects of a certain language
environment lang-env, use the command C-h L lang-env
<RET> (describe-language-environment). This tells you which
languages this language environment is useful for, and lists the
character sets, coding systems, and input methods that go with it. It
also shows some sample text to illustrate scripts used in this language
environment. By default, this command describes the chosen language
environment.
You can customize any language environment with the normal hook
set-language-environment-hook. The command
set-language-environment runs that hook after setting up the new
language environment. The hook functions can test for a specific
language environment by checking the variable
current-language-environment. This hook is where you should
put non-default settings for specific language environment, such as
coding systems for keyboard input and terminal output, the default
input method, etc.
Before it starts to set up the new language environment,
set-language-environment first runs the hook
exit-language-environment-hook. This hook is useful for undoing
customizations that were made with set-language-environment-hook.
For instance, if you set up a special key binding in a specific language
environment using set-language-environment-hook, you should set
up exit-language-environment-hook to restore the normal binding
for that key.
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