Recommended translation: "Cratylus," trans. C. D. C. Reeve in Plato: Complete Works, ed. J. M. Cooper (Hackett, 1997).  

Excerpt:

Hermogenes
Here is Socrates; shall we take him as a partner in our discussion?

Cratylus
If you like.

Hermogenes
Cratylus, whom you see here, Socrates, says that everything has a right name of its own, which comes by nature, and that a name is not whatever people call a thing by agreement, just a piece of their own voice applied to the thing, but that there is a kind of inherent correctness in names, which is the same for all men,both Greeks and barbarians.

Online:
Amazon (Recommended Translation)
Project Perseus (English, Free Access)
Project Perseus (Greek, Free Access)
Project Gutenberg (English, Free Access)