package require msgcat 1.5
::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::mcflset src-string ?translate-string?
::msgcat::mcflmset src-trans-list
::msgcat::mcunknown locale src-string ?arg arg ...?
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.
::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.
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 .MT (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.
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
Message files can be located in any directory, subject to the following conditions:
es.msg \(em spanish en_gb.msg \(em United Kingdom English
Exception: The message file for the root locale .MT 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.
namespace eval ::mypackage {
::msgcat::mcflset "Free Beer!" "Cerveza Gracias!"
}
If a package is installed into a subdirectory of the tcl_pkgPath and loaded via package require, the following procedure is recommended.
# 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
The message catalog code was developed by Mark Harrison.