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NAME

       msgcat - Tcl message catalog

SYNOPSIS

       package require Tcl 8.5

       package require msgcat 1.6

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

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

       ::msgcat::mcexists ?-exactnamespace? ?-exactlocale? src-string::msgcat::mclocale ?newLocale?

       ::msgcat::mcpreferences

       ::msgcat::mcloadedlocales subcommand ?locale?                                              │

       ::msgcat::mcload dirname

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

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

       ::msgcat::mcflset src-string ?translate-string?

       ::msgcat::mcflmset src-trans-list

       ::msgcat::mcunknown locale src-string ?arg arg ...?

       ::msgcat::mcpackagelocale subcommand ?locale?                                              │

       ::msgcat::mcpackageconfig subcommand option ?value?                                        │

       ::msgcat::mcforgetpackage
_________________________________________________________________________________________________

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 may be provided by adding a new file to
       the message catalog.

       msgcat  distinguises  packages by its namespace.  Each package has its own message catalog
       and configuration settings in msgcat.

       A locale is a specification string describing a user language like de_ch for Swiss German.
       In  msgcat,  there  is  a  global  locale  initialized by the system locale of the current
       system.  Each package may decide to use the global locale or to  use  a  package  specific
       locale.

       The  global  locale  may  be  changed  on demand, for example by a user initiated language
       change or within a multi user application like a web server.

COMMANDS

       ::msgcat::mc src-string ?arg arg ...?
              Returns a translation of src-string according to the 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::mcexists ?-exactnamespace? ?-exactlocale? src-string
              Return true, if there is a translation for the given src-string.                    │

              The  search  may be limited by the option -exactnamespace to only check the current │
              namespace and not any parent namespaces.                                            │

              It may also be limited by the option -exactlocale to only check the first  prefered │
              locale  (e.g. first element returned by ::msgcat::mcpreferences if global locale is │
              used).                                                                              │

       ::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.

              If the locale is set, the preference list of locales is evaluated.  Locales in this │
              list are loaded now, if not jet loaded.

       ::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::mcloadedlocales subcommand ?locale?
              This group of commands manage the list of loaded locales for packages not setting a
              package locale.

              The subcommand get returns the list of currently loaded locales.

              The subcommand present requires the argument  locale  and  returns  true,  if  this
              locale is loaded.

              The  subcommand  clear  removes  all  locales  and their data, which are not in the
              current preference list.

       ::msgcat::mcload dirname
              Searches the specified directory for files that match the  language  specifications │
              returned  by  ::msgcat::mcloadedlocales get (or msgcat::mcpackagelocale preferences │
              if a package locale is set) (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.                                                                 │

              In addition, the given folder is stored in the msgcat package configuration  option │
              mcfolder to eventually load message catalog files required by a locale change.

       ::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::mcflset src-string ?translate-string?
              Sets  the  translation  for src-string to translate-string in the current namespace
              for the locale implied by  the  name  of  the  message  catalog  being  loaded  via
              ::msgcat::mcload.   If  translate-string  is  not specified, src-string is used for
              both.  The function returns translate-string.

       ::msgcat::mcflmset src-trans-list
              Sets the translation for multiple source strings in src-trans-list in  the  current
              namespace  for  the  locale implied by the name of the message catalog being loaded
              via ::msgcat::mcload. src-trans-list must have an even number of elements and is in
              the   form   {src-string   translate-string   ?src-string   translate-string  ...?}
              ::msgcat::mcflmset  can  be  significantly  faster  than  multiple  invocations  of
              ::msgcat::mcflset. The function returns the number of translations set.

       ::msgcat::mcunknown locale src-string ?arg arg ...?
              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  passed  by  format  if  there  are  any  arguments.   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.                                          │

              Note  that  this  routine  is  only  called  if the concerned package did not set a │
              package locale unknown command name.                                                │

       ::msgcat::mcforgetpackage                                                                  │
              The calling package clears all its state within the msgcat  package  including  all │
              settings and translations.

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 and Cygwin, if none of those environment variables is set, msgcat will attempt
       to extract locale information from the registry.   From  Windows  Vista  on,  the  RFC4747
       locale    name   "lang-script-country-options"   is   transformed   to   the   locale   as
       "lang_country_script" (Example: sr-Latn-CS -> sr_cs_latin). For Windows XP,  the  language
       id  is  transformed analoguously (Example: 0c1a -> sr_yu_cyrillic).  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  the  unknown  handler  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 mcflset and mcflmset, 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::mcflset "Free Beer" "Cerveza Gratis"
              }

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.  Note  that  it  is  not  necessary  to  pass  the  output  of
       ::msgcat::mc  to format directly; by passing the values to substitute in as arguments, the
       formatting substitution is done directly.

              msgcat::mc {Produced %1$d at %2$s} $num $city
              # ... where that key is mapped to one of the
              # human-oriented versions by msgcat::mcset

Package private locale                                                                            │
       A package using msgcat may choose to use its own package private locale and its own set of │
       loaded locales, independent to the global locale set by ::msgcat::mclocale.                │

       This  allows a package to change its locale without causing any locales load or removal in │
       other packages and not to invoke the global locale change callback (see below).            │

       This action is controled by the following ensemble:                                        │

       ::msgcat::mcpackagelocale set ?locale?                                                     │
              Set or change a package private locale.  The package private locale is set  to  the │
              given  locale  if  the  locale  is  given.   If the option locale is not given, the │
              package is set to package private locale mode, but no locale is  changed  (e.g.  if │
              the  global  locale  was  valid for the package before, it is copied to the package │
              private locale).                                                                    │

              This command may cause the load of locales.                                         │

       ::msgcat::mcpackagelocale get                                                              │
              Return the package private locale or the  global  locale,  if  no  package  private │
              locale is set.                                                                      │

       ::msgcat::mcpackagelocale preferences                                                      │
              Return  the  package  private  preferences or the global preferences, if no package │
              private locale is set.                                                              │

       ::msgcat::mcpackagelocale loaded                                                           │
              Return the list of locales loaded for this package.                                 │

       ::msgcat::mcpackagelocale isset                                                            │
              Returns true, if a package private locale is set.                                   │

       ::msgcat::mcpackagelocale unset                                                            │
              Unset the package private locale and use  the  globale  locale.   Load  and  remove │
              locales  to  adjust the list of loaded locales for the package to the global loaded │
              locales list.                                                                       │

       ::msgcat::mcpackagelocale present locale                                                   │
              Returns true, if the given locale is loaded for the package.                        │

       ::msgcat::mcpackagelocale clear                                                            │
              Clear any loaded locales of the package not present in the package preferences.     │

Changing package options                                                                          │
       Each package using msgcat has a set of options within msgcat.   The  package  options  are │
       described  in  the  next  sectionPackage options.  Each package option may be set or unset │
       individually using the following ensemble:                                                 │

       ::msgcat::mcpackageconfig get option                                                       │
              Return the current value of the given option.  This call returns an  error  if  the │
              option is not set for the package.                                                  │

       ::msgcat::mcpackageconfig isset option                                                     │
              Returns 1, if the given option is set for the package, 0 otherwise.                 │

       ::msgcat::mcpackageconfig set option value                                                 │
              Set  the  given  option  to the given value.  This may invoke additional actions in │
              dependency of the option.  The return value is 0 or the number of  loaded  packages │
              for the option mcfolder.                                                            │

       ::msgcat::mcpackageconfig unset option                                                     │
              Unsets  the  given option for the package.  No action is taken if the option is not │
              set for the package.  The empty string is returned.                                 │

   Package options                                                                                │
       The following package options are available for each package:                              │

       mcfolder                                                                                   │
              This is the message folder of the package. This option is set by mcload and by  the │
              subcommand  set.  Both  are  identical and both return the number of loaded message │
              catalog files.                                                                      │

              Setting or changing this value will load all locales contained in  the  preferences │
              valid for the package. This implies also to invoke any set loadcmd (see below).     │

              Unsetting this value will disable message file load for the package.                │

       loadcmd                                                                                    │
              This  callback  is invoked before a set of message catalog files are loaded for the │
              package which has this property set.                                                │

              This callback may be used to do any preparation work for message file  load  or  to │
              get the message data from another source like a data base. In this case, no message │
              files are used (mcfolder is unset).                                                 │

              See section callback  invocation  below.   The  parameter  list  appended  to  this │
              callback is the list of locales to load.                                            │

              If  this  callback  is  changed,  it  is  called with the preferences valid for the │
              package.                                                                            │

       changecmd                                                                                  │
              This callback is invoked when a default local change was performed. Its purpose  is │
              to  allow a package to update any dependency on the default locale like showing the │
              GUI in another language.                                                            │

              See the callback invocation section below.  The parameter  list  appended  to  this │
              callback  is  mcpreferences.  The registered callbacks are invoked in no particular │
              order.                                                                              │

       unknowncmd                                                                                 │
              Use a package locale mcunknown procedure instead of the standard  version  supplied │
              by the msgcat package (msgcat::mcunknown).                                          │

              The  called  procedure  must  return  the  formatted  message which will finally be │
              returned by msgcat::mc.                                                             │

              A generic unknown handler is used if set to the  empty  string.  This  consists  in │
              returning  the  key if no arguments are given. With given arguments, format is used │
              to process the arguments.                                                           │

              See section callback invocation below.  The appended  arguments  are  identical  to │
              ::msgcat::mcunknown.                                                                │

   Callback invocation                                                                            │
       A package may decide to register one or multiple callbacks, as described above.            │

       Callbacks are invoked, if:                                                                 │

       1. the callback command is set,                                                            │

       2. the command is not the empty string,                                                    │

       3. the registering namespace exists.                                                       │

       If  a  called  routine  fails  with  an  error, the bgerror routine for the interpreter is │
       invoked after command completion.  Only exception is the  callback  unknowncmd,  where  an │
       error causes the invoking mc-command to fail with that error.                              │

   Examples                                                                                       │
       Packages  which display a GUI may update their widgets when the global locale changes.  To │
       register to a callback, use:                                                               │
              namespace eval gui {                                                                │
                  msgcat::mcpackageconfig changecmd updateGUI                                     │

                  proc updateGUI args {                                                           │
                      puts "New locale is '[lindex $args 0]'."                                    │
                  }                                                                               │
              }                                                                                   │
              % msgcat::mclocale fr                                                               │
              fr                                                                                  │
              % New locale is 'fr'.                                                               │

       If locales (or additional locales) are contained in another source like  a  data  base,  a │
       package may use the load callback and not mcload:                                          │
              namespace eval db {                                                                 │
                  msgcat::mcpackageconfig loadcmd loadMessages                                    │

                  proc loadMessages args {                                                        │
                      foreach locale $args {                                                      │
                          if {[LocaleInDB $locale]} {                                             │
                              msgcat::mcmset $locale [GetLocaleList $locale]                      │
                          }                                                                       │
                      }                                                                           │
                  }                                                                               │
              }                                                                                   │

       The  clock  command  implementation  uses  msgcat  with  a package locale to implement the │
       command line parameter -locale.  Here are some sketches of the implementation:             │

       First, a package locale is initialized and the generic unknown function is desactivated:   │
              msgcat::mcpackagelocale set                                                         │
              msgcat::mcpackageconfig unknowncmd ""                                               │
       As an example, the user requires the week day in a certain locale as follows:              │
              clock format [clock seconds] -format %A -locale fr                                  │
       clock sets the package locale to fr and looks for the day name as follows:                 │
              msgcat::mcpackagelocale set $locale                                                 │
              return [lindex [msgcat::mc DAYS_OF_WEEK_FULL] $day]                                 │
              ### Returns "mercredi"                                                              │
       Within clock, some message-catalog items are heavy in computation and thus are dynamically │
       cached using:                                                                              │
              proc ::tcl::clock::LocalizeFormat { locale format } {                               │
                  set key FORMAT_$format                                                          │
                  if { [::msgcat::mcexists -exactlocale -exactnamespace $key] } {                 │
                      return [mc $key]                                                            │
                  }                                                                               │
                  #...expensive computation of format clipped...                                  │
                  mcset $locale $key $format                                                      │
                  return $format                                                                  │
              }                                                                                   │

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