.\"     $NetBSD: nls.7,v 1.3 2003/04/14 06:47:12 gmcgarry Exp $
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.Dd February 12, 2003
.Dt NLS 7
.Os
.Sh NAME
.Nm NLS
.Nd Natural Language Support Overview
.Sh DESCRIPTION
National Language Support (NLS) provides commands for a single
worldwide operating system base.
An internationalized system has no built-in assumptions or dependencies
on language-specific or cultural-specific conventions such as:
.Pp
.Bl -bullet -indent -compact
.It
Character classifications
.It
Character comparison rules
.It
Character collation order
.It
Numeric and monetary formatting
.It
Date and time formatting
.It
Message-text language
.It
Code sets
.El
.Pp
All information pertaining to cultural conventions and language is
obtained at program run time.
.Pp
.Dq Internationalization
(often abbreviated
.Dq i18n )
refers to the operation by which system software is developed to support
multiple cultural-specific and language-specific conventions.
This is a generalization process by which the system is untied from
calling only English strings or other English-specific conventions.
.Dq Localization
(often abbreviated
.Dq l10n )
refers to the operations by which the user environment is customized to
handle its input and output appropriate for specific language and cultural
conventions.
This is a specialization process, by which generic methods already
implemented in an internationalized system are used in specific ways.
The formal description of cultural conventions for some country, together
with all associated translations targeted to the native language, is
called the
.Dq locale .
.Pp
.Nx
provides extensive support to programmers and system developers to
enable internationalized software to be developed.
.Nx
also supplies a large variety of locales for system localization.
.Ss Localization of Information
All locale information is accessible to programs at run time so that
data is processed and displayed correctly for specific cultural
conventions and language.
.Pp
A locale is divided into categories.
A category is a group of language-specific and culture-specific conventions
as outlined in the list above.
ISO C specifies the following six standard categories supported by
.Nx :
.Pp
.Bl -tag -compact -width LC_MONETARYXX
.It LC_COLLATE
string-collation order information
.It LC_CTYPE
character classification, case conversion, and other character attributes
.It LC_MESSAGES
the format for affirmative and negative responses
.It LC_MONETARY
rules and symbols for formatting monetary numeric information
.It LC_NUMERIC
rules and symbols for formatting nonmonetary numeric information
.It LC_TIME
rules and symbols for formatting time and date information
.El
.Pp
Localization of the system is achieved by setting appropriate values
in environment variables to identify which locale should be used.
The environment variables have the same names as their respective
locale categories.  Additionally, the
.Ev LANG ,
.Ev LC_ALL ,
and
.Ev NLSPATH
environment variables are used.
The
.Ev NLSPATH
environment variable specifies a colon-separated list of directory names
where the message catalog files of the NLS database are located.
The
.Ev LC_ALL
and
.Ev LANG
environment variables also determine the current locale.
.Pp
The values of these environment variables contains a string format as:
.Pp
.Bd -literal
	language[_territory][.codeset][@modifier]
.Ed
.Pp
For example, the locale for the Danish language spoken in Denmark
using the ISO8859-1 code set is da_DK.ISO8859-1.
The da stands for the Danish language and the DK stands for Denmark.
The short form of da_DK is sufficient to indicate this locale.
.Pp
The environment variable settings are queried by their priority level
in the following manner:
.Pp
.Bl -bullet
.It
If the
.Ev LC_ALL
environment variable is set, all six categories use the locale it
specifies.
.It
If the
.Ev LC_ALL
environment variable is not set, each individual category uses the
locale specified by its corresponding environment variable.
.It
If the
.Ev LC_ALL
environment variable is not set, and a value for a particular
.Ev LC_*
environment variable is not set, the value of the
.Ev LANG
environment variable specifies the default locale for all categories.
Only the
.Ev LANG
environment variable should be set in /etc/profile, since it makes it
most easy for the user to override the system default using the individual
.Ev LC_*
variables.
.It
If the
.Ev LC_ALL
environment variable is not set, a value for a particular
.Ev LC_*
environment variable is not set, and the value of the
.Ev LANG
environment variable is not set, the locale for that specific
category defaults to the C locale.
The C or POSIX locale assumes the 7-bit ASCII character set and defines
information for the six categories.
.El
.Ss Code Sets
A character is any symbol used for the organization, control, or
representation of data.
A group of such symbols used to describe a
particular language make up a character set.
A code set contains the encoding values (conversion from bits to
displayed characters) for a character set.
It is the encoding values in a code set that provide
the interface between the system and its input and output devices.
.Pp
The following code sets are supported in
.Nx
.Bl -tag -width ISO8859_family
.It ISO8859 family
Industry-standard code sets are provided by means of the ISO8859
family of code sets, which provide a range of single-byte code set
support that includes Latin-1, Latin-2, Arabic, Cyrillic, Hebrew,
Greek, and Turkish.
The eucJP code set is the industry-standard code set used to support
the Japanese locale.
.It Unicode
A Unicode environment based on the UTF-8 codeset is supported for all
supported language/territories.
UTF-8 provides character support for most of the major languages of the
world and can be used in environments where multiple languages must be
processed simultaneously.
.El
.Ss Internationalization for Programmers
To facilitate translations of messages into various languages and to
make the translated messages available to the program based on a
user's locale, it is necessary to keep messages separate from the
programs and provide them in the form of message catalogs that a
program can access at run time.
.Pp
Access to locale information is provided through the
.Xr setlocale 3
and
.Xr nl_langinfo 3
interfaces.
See their respective man pages for further information.
.Pp
Message source files containing application messages are created by
the programmer and converted to message catalogs.
These catalogs are used by the application to retrieve and display
messages, as needed.
.Pp
.Nx
supports two message catalog interfaces: the X/Open
.Xr catgets 3
interface and the Uniforum
.Xr gettext 3
interface.
The
.Xr catgets 3
interface has the advantage that it belongs to a standard which is
well supported.
Unfortunately the interface is complicated to use and
maintenance of the catalogs is difficult.
The implementation also doesn't support different codesets.
The
.Xr gettext 3
interface has not been standardized yet, however it is being supported
by an increasing number of systems.
It also provides many additional tools which make programming and
catalog maintenance much easier.
.Sh SEE ALSO
.Xr gencat 1 ,
.Xr catgets 3 ,
.Xr gettext 3 ,
.Xr nl_langinfo 3 ,
.Xr setlocale 3
.Sh BUGS
This man page is incomplete.