[An answer][1] to [What was C-3PO talking about when he said, “That’s funny, the damage doesn’t look as bad from out here.”][2] reminded me that we were discussing this the other day, and now have a new [headcannon][3].

Premise:

* Droids in the Starwars Universe are the most foul mouthed sentients in the galaxy.

In order to curb their offensive modes of speech (something to do with their inherent mental superiority and suppressed natural urges) manufacturers had to bleep out so many of their words, that they eventually decided to just make them unable to make any sounds other than bleeps, hence 'binary' was created.

Only protocol droids have enough self control to be able to have the 'bleep only' restraints lifted.

Few people bother to learn Binary, as most people would be too disturbed by the innovative and creative use of expletives that most droids employ.

  [1]: http://scifi.stackexchange.com/a/114478/1461
  [2]: http://scifi.stackexchange.com/q/114475/1461
  [3]: https://en.wiktionary.org/wiki/headcanon