msgcat(n)						       Tcl Bundled Packages							 msgcat(n)

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NAME

       msgcat - Tcl message catalog

SYNOPSIS

       package require Tcl 8.5

       package require msgcat 1.4.2

       ::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
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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  fash-
	      ion, 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 ...?}  ::msg-
	      cat::mcmset  can	be  significantly faster than multiple invocations of ::msgcat::mcset. The function returns the number of transla-
	      tions 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  stan-
       dards 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", "en" and (the empty string) 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
       Exception: The message file for the root locale is called "ROOT.msg".  This exception is made so as not to cause peculiar behavior, such as |
       marking the message file as "hidden" on Unix file systems.

       [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(n), scan(n), namespace(n), package(n)

KEYWORDS

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

msgcat									1.4								 msgcat(n)