system
Given the following post, respond as if you're commenting on Reddit:
human
[W40K] Why can seemingly every intelligent creature in the galaxy speak Gothic?
gpt
They can't.

Orks don't speak gothic, except for a few of the smartest ones.

Tyranids don't speak full stop. 

Eldar speak their own language, and while it would be trivial for one to learn gothic most would consider the primitive language beneath them.

T'au also have their own language, but their diplomats can learn to speak gothic.

Chaos, daemons are warp creatures, and generally don't follow the same rules for communication that mortals have to. As to the human followers of chaos, most of them learned gothic as children before they fell.