Babel-17

Nebula Award: Best Novel winner (1967).
Hugo Award: Best Novel nominee (1967).

In warfare, as in all organized endeavor, communication is the keystone of success: if your enemy can thoroughly disrupt your data-flow, then you are lost. The alien invaders could do just that with BABEL-17.

So General Forester had to travel down to the bizarre depths of Transport Town in search of the Cosmic Poetess whose mind encompassed all tongues. For if she could not discern the inner meaning of the aliens' weird communication weapon, the Human Race and all its works must perish...