msgcat(n)                    Tcl Bundled Packages                    msgcat(n)


       msgcat - Tcl message catalog

       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::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?                     │


       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

       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

       ::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      │

              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.

       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


       to extract its parts.  The initial locale is then set by calling
       ::msgcat::mclocale with the argument


       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.

       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

       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

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

       [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

       [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"

       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]

       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                                               │
              }                                                                │

       The message catalog code was developed by Mark Harrison.

       format(n), scan(n), namespace(n), package(n)

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

msgcat                                1.5                            msgcat(n)