A message catalog is a list of messages that your application will display. The main idea is that you can maintain several catalogs, one for each language you support. Unfortunately, you have to be explicit about using message catalogs. Everywhere you generate output or display strings in Tk widgets, you need to change your code to go through a message catalog. Fortunately, Tcl uses a nice trick to make this fairly easy and to keep your code readable. Instead of using keys like “message42” to get messages out of the catalog, Tcl just uses the strings you would use by default. For example, instead of this code:
puts "Hello, World!"
A version that uses message catalogs looks like this:
puts [msgcat::mc "Hello, World!"]
If you ...