It's TypeScript with the addition of a few key features that are helpful for Angular's design.
Technically, Angular 1.0 also had its own scripting language too. It's kind of inevitable, since Javascript itself is one of the obstacles to making a better web framework.
I think it is more Dart... At least the AtScript specification mentions Dart more often than any other language.
The language is layered on top of Javascript and is completely optional.
It's not new language, just syntax sugar. And optional.
It's utterly insane. Just as in AngularJS 1.3 they have invented there own expression language which floats around in HTML attributes, thereby eliminating the use of Javascript itself and all it's functional goodness. And worst, the user has to incur the cost of downloading this needless code for the expression language to bootstrap the framework.