Now I Am Become Death, the Destroyer of Worlds
— J. Robert Oppenheimer
Oppenheimer famously quoted this from The Bhagavad Geeta in the context of the nuclear bomb. The way this sentence is structured feels weird to me. “Now I am Death” or “Now I have become Death” sound much more natural in English to me.
Was he trying to simulate some formulation in Sanskrit that is not available in the English language?
It's from English, not Sanskrit. More specifically, an archaic English feature, where you'd use "be" instead of "have" for the present tense, if the main verb denotes a change of state (such as "become"). Note how "I have become Death" sounds perfectly fine for modern readers.
Odds are that Oppenheimer was quoting either an archaic translation Bhagavad Gita, or one using archaic language (this is typical for religious texts).
Also give this a check. English used to follow similar rules for be/have as German does for sein/haben.
[Shameless community promotion: check !linguistics@lemmy.ml ! This sort of question would fit like a glove there.]