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!"