msgcat(3tcl)
NAME
msgcat - Tcl message catalog
SYNOPSIS
package require Tcl 8.5 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 ...? ______________________________________________________________________________
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::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.
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 ::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 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
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
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