Originally Posted by NCC-73515
Then why do all Starfleet vessels have furniture, signs, consoles for humans and english letters on the hull?
I believe that standard signage arose as a consequence of Starfleet's genesis on Earth. In any case, it would be necessary for any such peace-keeping force to have a standardized language, to ensure equal communication among all members of the force.
As for interior design, that's easily explained by the simple fact that most Federation member worlds are inhabited by humanoids. I'm pretty sure that if you saw a Starfleet ship crewed mostly by Rakelli (just for argument’s sake) that the interior would be suitably adapted.