For well over a year Drupal core has supported much more advanced multilingual capabilities compared to previous versions. When Drupal 6 landed all the hard work that Gábor Hojtsy and the internationalization team did was released to the world and people rejoiced (in 60+ languages).
This is a very broad simplification of what was done, but the focus of those efforts was to make it easier for administrators to translate content (nodes) on a site. If you have a news story published in English you can create a French version of that news story that is 'tied' to the English story and it will be easy for your site visitors to switch between the English and French (or Spanish or Dutch etc.) version of your story.
As I said, this is a very broad simplification. There was much more work being done, but not all of it managed to make it into core. Some translations features were left in the contributed i18n (internationalization) module. Others features were 'roughed in' to core to allow for future improvements.
One such feature that didn't quite get finished was menu translations.
Menus can be translated, but its not entirely obvious how to do it. And even after you've read the documentation, it may not necessarily work the way you expect it to. (See example: Menu items disappear when you change language in the Drupal handbook.)