You can internationalize your source code manually or automatically (internationalization code is automatically generated on programs that have already been written).
With the automatic generation of internationalization strings, the IDE searches for every occurence of a quoted text string and replaces it with a method call (getString(key)). At the same time, the string is added to the resource bundle, code is generated in the source file to access the string's value in the resource bundle. You are stepped through the source code until all the strings that require internationalization have been found and changed. You can skip over strings that you do not want to internationalize.
In addition to creating internationalized strings, you can also check resource bundles for strings to internationalize with the Internationalization Test Wizard.
For information on how to internationalize source code, see:
Generating Internationalization Strings Automatically
Inserting Internationalized Strings Into Source Code
Setting Internationalization Strings With the Form Editor
Testing Bundles for Internationalized Strings
For information on properties files and locales, see:
Setting Properties Files