The work on I18Nv2 has actually started as a refactoring of I18N, but after some time I figured out that too many BC breaking changes were applied, so the release of a new major version was suggested.
I18N was modeled after Java OO practice and it provides a bunch of classes for each formatting action (numbers, currencies, dates).
I18Nv2 takes another approach and provides all formatting functionality within one class, which is I18Nv2_Locale.
I wouldn't say I18Nv2's approach is the better one, because it depends on the internationalization capabilities of the underlying operating system, but it's simpler and faster - though it is in need of user contributed date and time formatting rules.
I18N's translation functionality was dropped in favour of the new and shiny Translation2.
I18Nv2 still provides an HTTP negotiator to reveal the users preferred language/locale and charset.