Sign Language is for people who cannot hear, so a "language" is created to communicate with them. The way to solve Gordon's problem is an electrolarynx [http://en.wikipedia.org/wiki/Mechanical_larynx], ala Ned from South Park. Since his ears clearly work just fine (unless he's an amazing lip reader, though any radio-given instructions at any point in the games would nullify that theory), there would be no need for him to learn an entirely new language.wordsmith said:er... guys... You remember that Gordon can't talk, right? And they're introducing sign language to allow a non-talking character to communicate? 2 and 2 make.... anyone?
Edit: Also, I'm fairly... uneasy about this. Firstly, and I'm aware that there's probably more than this, but I don't like that a 3 hour game is being set back by years with one of the reasons being that they need to learn a new language. Secondly, it was awkward enough when they added that pompous what's-his-face in Episode 2, now they're adding more characters? Couldn't it have waited until Half Life 3 to introduce more characters? And thirdly, while I respect that they're adding this character to make the game seem more open to the handicapped, it always feels gimmicky when a character is boiled-down to "token minority" character with little else interesting about the character beyond that, especially when the character is coming from out of left field right at the end of a story.
I have nothing against the addition really, but Valve might have their work cut-out for them to make this character fit into a story that's already mostly over, and it would be a shame for the deaf character to turn-out to be little more than a gimmick to sell a few more copies of the game to handicapped individuals.