When you create a new Knowledge Base or open an existing one, a set of predefined String constants and Languages are created in it (or updated if they already existed). They are used in the generated code for messages, button captions, labels, etc.
You can view the predefined languages in the KB Explorer, in the localization node (under customization):

GeneXus provides a cross reference to where String constants are used.
Several options for language management are included.
- Include GeneXus Messages --> Include the GeneXus messages in the XPZ.
- Include Untranslated Messages --> Include the untranslated messages in the XPZ.