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NAME

       msgcat - Tcl message catalog

SYNOPSIS

       package require Tcl 8.2

       package require msgcat 1.3.4

       ::msgcat::mc src-string ?arg arg ...?

       ::msgcat::mcmax ?src-string src-string ...?

       ::msgcat::mclocale ?newLocale?

       ::msgcat::mcpreferences

       ::msgcat::mcload dirname

       ::msgcat::mcset locale src-string ?translate-string?

       ::msgcat::mcmset locale src-trans-list

       ::msgcat::mcunknown locale src-string
_________________________________________________________________

DESCRIPTION

       The  msgcat  package  provides a set of functions that can be used to manage multi-lingual
       user interfaces.  Text strings are defined in a ``message catalog'' which  is  independent
       from  the  application,  and  which  can  be  edited  or  localized  without modifying the
       application source code.  New languages or locales are provided by adding a  new  file  to
       the message catalog.

       Use of the message catalog is optional by any application or package, but is encouraged if
       the application or package wishes to be enabled for multi-lingual applications.

COMMANDS

       ::msgcat::mc src-string ?arg arg ...?
              Returns a translation of src-string according to the  user's  current  locale.   If
              additional  arguments  past  src-string  are  given,  the format command is used to
              substitute the additional arguments in the translation of src-string.

       ::msgcat::mc will search the messages defined in the current namespace for  a  translation
       of  src-string;  if  none is found, it will search in the parent of the current namespace,
       and so on until it reaches  the  global  namespace.   If  no  translation  string  exists,
       ::msgcat::mcunknown  is  called  and  the  string  returned  from  ::msgcat::mcunknown  is
       returned.

       ::msgcat::mc is the main function used to localize an application.  Instead  of  using  an
       English  string  directly, an application can pass the English string through ::msgcat::mc
       and use the result.  If an application is written for a single language in  this  fashion,
       then  it  is  easy  to  add  support for additional languages later simply by defining new
       message catalog entries.

       ::msgcat::mcmax ?src-string src-string ...?
              Given several source strings, ::msgcat::mcmax returns the  length  of  the  longest
              translated string.  This is useful when designing localized GUIs, which may require
              that all buttons, for example, be a fixed width (which will be  the  width  of  the
              widest button).

       ::msgcat::mclocale ?newLocale?
              This  function  sets the locale to newLocale.  If newLocale is omitted, the current
              locale is returned, otherwise the current  locale  is  set  to  newLocale.   msgcat
              stores and compares the locale in a case-insensitive manner, and returns locales in
              lowercase.  The initial locale is determined by the locale specified in the  user's
              environment.  See LOCALE SPECIFICATION below for a description of the locale string
              format.

       ::msgcat::mcpreferences
              Returns an ordered list of the locales preferred by the user, based on  the  user's
              language   specification.   The  list  is  ordered  from  most  specific  to  least
              preference.  The list  is  derived  from  the  current  locale  set  in  msgcat  by
              ::msgcat::mclocale,  and  cannot be set independently.  For example, if the current
              locale is en_US_funky, then ::msgcat::mcpreferences returns {en_US_funky en_US en}.

       ::msgcat::mcload dirname
              Searches the specified directory for files that match the  language  specifications
              returned  by  ::msgcat::mcpreferences (note that these are all lowercase), extended
              by the file extension ``.msg''.  Each matching file is read in  order,  assuming  a
              UTF-8  encoding.  The file contents are then evaluated as a Tcl script.  This means
              that Unicode characters may be present in the message file either directly in their
              UTF-8  encoded  form,  or  by  use  of  the  backslash-u  quoting recognized by Tcl
              evaluation.  The number of message files which matched the specification  and  were
              loaded is returned.

       ::msgcat::mcset locale src-string ?translate-string?
              Sets the translation for src-string to translate-string in the specified locale and
              the current namespace.  If translate-string is not specified,  src-string  is  used
              for both.  The function returns translate-string.

       ::msgcat::mcmset locale src-trans-list
              Sets the translation for multiple source strings in src-trans-list in the specified
              locale and the current namespace.  src-trans-list  must  have  an  even  number  of
              elements  and  is  in  the form {src-string translate-string ?src-string translate-
              string ...?} ::msgcat::mcmset can be significantly faster than multiple invocations
              of ::msgcat::mcset. The function returns the number of translations set.

       ::msgcat::mcunknown locale src-string
              This  routine  is  called  by  ::msgcat::mc in the case when a translation for src-
              string is not defined in the current locale.  The default action is to return  src-
              string.   This  procedure  can  be redefined by the application, for example to log
              error messages for each  unknown  string.   The  ::msgcat::mcunknown  procedure  is
              invoked at the same stack context as the call to ::msgcat::mc.  The return value of
              ::msgcat::mcunknown is used as the return value for the call to ::msgcat::mc.

LOCALE SPECIFICATION

       The locale is specified to msgcat by a locale string passed  to  ::msgcat::mclocale.   The
       locale  string  consists  of  a  language  code, an optional country code, and an optional
       system-specific code, each separated  by  ``_''.   The  country  and  language  codes  are
       specified  in  standards  ISO-639  and ISO-3166.  For example, the locale ``en'' specifies
       English and ``en_US'' specifies U.S. English.

       When the msgcat package is first loaded, the locale is initialized according to the user's
       environment.   The  variables env(LC_ALL), env(LC_MESSAGES), and env(LANG) are examined in
       order.  The first of them to have a non-empty value  is  used  to  determine  the  initial
       locale.  The value is parsed according to the XPG4 pattern
              language[_country][.codeset][@modifier]
       to  extract  its parts.  The initial locale is then set by calling ::msgcat::mclocale with
       the argument
              language[_country][_modifier]
       On Windows, if none of those environment variables is set, msgcat will attempt to  extract
       locale information from the registry.  If all these attempts to discover an initial locale
       from the user's environment fail, msgcat defaults to an initial locale of ``C''.

       When a locale is specified by the user, a ``best match'' search is performed during string
       translation.   For  example, if a user specifies en_GB_Funky, the locales ``en_GB_Funky'',
       ``en_GB'', and ``en'' are searched in order until a matching translation string is  found.
       If no translation string is available, then ::msgcat::mcunknown is called.

NAMESPACES AND MESSAGE CATALOGS

       Strings stored in the message catalog are stored relative to the namespace from which they
       were added.  This allows multiple packages  to  use  the  same  strings  without  fear  of
       collisions  with  other packages.  It also allows the source string to be shorter and less
       prone to typographical error.

       For example, executing the code
              ::msgcat::mcset en hello "hello from ::"
              namespace eval foo {
                 ::msgcat::mcset en hello "hello from ::foo"
              }
              puts [::msgcat::mc hello]
              namespace eval foo {puts [::msgcat::mc hello]}
       will print
              hello from ::
              hello from ::foo

       When searching for a translation of a message, the message catalog will search  first  the
       current  namespace,  then  the parent of the current namespace, and so on until the global
       namespace is reached.  This allows child  namespaces  to  "inherit"  messages  from  their
       parent namespace.

       For example, executing (in the ``en'' locale) the code
              ::msgcat::mcset en m1 ":: message1"
              ::msgcat::mcset en m2 ":: message2"
              ::msgcat::mcset en m3 ":: message3"
              namespace eval ::foo {
                 ::msgcat::mcset en m2 "::foo message2"
                 ::msgcat::mcset en m3 "::foo message3"
              }
              namespace eval ::foo::bar {
                 ::msgcat::mcset en m3 "::foo::bar message3"
              }
              namespace import ::msgcat::mc
              puts "[mc m1]; [mc m2]; [mc m3]"
              namespace eval ::foo {puts "[mc m1]; [mc m2]; [mc m3]"}
              namespace eval ::foo::bar {puts "[mc m1]; [mc m2]; [mc m3]"}
       will print
              :: message1; :: message2; :: message3
              :: message1; ::foo message2; ::foo message3
              :: message1; ::foo message2; ::foo::bar message3

LOCATION AND FORMAT OF MESSAGE FILES

       Message files can be located in any directory, subject to the following conditions:

       [1]    All message files for a package are in the same directory.

       [2]    The  message  file  name  is  a msgcat locale specifier (all lowercase) followed by
              ``.msg''.  For example:
              es.msg    -- spanish
              en_gb.msg -- United Kingdom English

       [3]    The file contains a series of calls to mcset  and  mcmset,  setting  the  necessary
              translation  strings  for the language, likely enclosed in a namespace eval so that
              all source strings are tied to the namespace of the package. For example,  a  short
              es.msg might contain:
              namespace eval ::mypackage {
                 ::msgcat::mcset es "Free Beer!" "Cerveza Gracias!"
              }

RECOMMENDED MESSAGE SETUP FOR PACKAGES

       If  a  package  is installed into a subdirectory of the tcl_pkgPath and loaded via package
       require, the following procedure is recommended.

       [1]    During  package  installation,  create  a  subdirectory  msgs  under  your  package
              directory.

       [2]    Copy your *.msg files into that directory.

       [3]
               Add the following command to your package initialization script:
              # load language files, stored in msgs subdirectory
              ::msgcat::mcload [file join [file dirname [info script]] msgs]

POSITIONAL CODES FOR FORMAT AND SCAN COMMANDS

       It is possible that a message string used as an argument to format might have positionally
       dependent parameters that might need  to  be  repositioned.   For  example,  it  might  be
       syntactically desirable to rearrange the sentence structure while translating.
              format "We produced %d units in location %s" $num $city
              format "In location %s we produced %d units" $city $num

       This can be handled by using the positional parameters:
              format "We produced %1\$d units in location %2\$s" $num $city
              format "In location %2\$s we produced %1\$d units" $num $city

       Similarly,   positional   parameters  can  be  used  with  scan  to  extract  values  from
       internationalized strings.

CREDITS

       The message catalog code was developed by Mark Harrison.

SEE ALSO

       format(3tcl), scan(3tcl), namespace(3tcl), package(3tcl)

KEYWORDS

       internationalization, i18n, localization, l10n, message, text, translation