I just found this blog post on David Haywood's blog of MAME development.

The highlights:

In 1981 Stern started work on Moon War, with SPEECH, just like Berzerk, but apparently felt the game too primitive.

So they turned around and created a "MW2" board, the released Moon War, sadly now without speech.

The blog post also covers a German release of Berzerk, with "the Robots sound even more intimidating when they speak in German!"