[could someone write some words here about what message catalogs are, as well as some of the facilities that exist for creation and use of them?]
Tcl programmers can use message catalogs to create applications
that are language-independent. Through the use of message cata-
logs, prompts, messages, menus and so forth can exist for any
number of languages, and they can altered, and new languages
added, without affecting any Tcl or C source code, greatly eas-
ing the maintenance difficulties incurred by supporting multiple
languages.
A default text message is passed to the command that fetches
entries from message catalogs. This allows the Tcl programmer to
create message catalogs containing messages in various languages,
but still have a set of default messages available regardless of
the presence of any message catalogs, and allow the programs to
press on without difficulty when no catalogs are present.
Thus, the normal approach to using message catalogs is to ignore
errors on catopen, in which case catgets will return the default
message that was specified in the call.
The Tcl message catalog commands normally ignore most errors. If
it is desirable to detect errors, a special option is provided.
This is normally used only during debugging, to insure that mes-
sage catalogs are being used. If your Unix implementation does
not have XPG/3 message catalog support, stubs will be compiled in
that will create a version of catgets that always returns thedefault string. This allows for easy porting of software to environments that don't have support for message catalogs.
Message catalogs are global to the process, an application with multiple Tcl interpreters within the same process may pass and share message catalog handles.