Babel-17

The commander of the Earthpeople’s Alliance journeyed into the bizarre depths of Transport Town to seek Rydra Wong, the cosmic poetess whose words reached across space and whose mind could perceive the meaning of all the world’s tongues. And his request placed her into the heart of the vile interstellar war between the Alliance and the Invaders.
The new weapon of the Invaders was Babel-17, a menacing hum clogging up Alliance space communications. Rydra had to decipher the communications power of Babel-17 before it could lead to intergalactic defeat. And to do that, she would have to be the target of the next outer-space attack.