No subject

default language and localizations. If a page is translated, the
translated page title appears correctly in the translated language 
as navigation title and you need a different navigation title only
- in default language or localizations - if the page title for 
any reason (i.e. length) won't suit to your needs in the navigation.

As a consequence it is as important in the default language as in
localizations to have the possibilty to add naviagtion titles.

Mathias