The localized text is stored in two types of files, DTD files, and properties files. The DTD files have a dtd extension and contain entity declarations, one for each text string that is used in a window. For example, the file messenger.dtd contains entity declarations for each menu command. In addition, keyboard shortcuts for each command are also defined, because they may be different for each language. DTD files are used by XUL files, so in general, you will have one per XUL file.
Properties files are similar, but are used by script files.
The file messenger.properties contains a few such strings. This structure means that to turn Mozilla or a component into a different language, one only needs to add a new locale for that language. Other Packages Many of the packages in Mozilla are sub-packages of the communicator package. For example, you'll find the bookmarks window, the history viewer and the preferences dialogs within the communicator package. They are put there because they are general to a number of packages.