*Warning: Spoilers ahead*
If the sound of crackling ice were a language, it would be the White Walkers'. But, alas, the decision to take away the voice of the (growing) majority was made early on.
According to Vanity Fair, who recently combed through the Game of Thrones scripts that are on display at the Writers Guild of America West library, showrunners D.B. Weiss and David Benioff originally wrote the language into the show, but then it got scrapped.
In the show's pilot, the scripts say the Army of the Dead calls out in “inhuman shrieks” and “a chilling sound like crackling ice,” the same way George R.R. Martin’s books describe their native tongue. “These are not the noises of mindless predators. This is a language and whatever is speaking is getting closer,” the script reads. (*Shivers*)
Even GoT language expert David Peterson, who created the Dothraki and Valyrian languages for the show, invented a language for the White Walkers. It was called Skroth (which, TBH, seems like the perfect mix of skull and goth, and exactly how we picture the Night King in his teen years), but it ended up being cut from the pilot and replaced with the literal sound of cracking ice.
“I think ultimately they decided they didn’t want them actually saying stuff and even subtitle it. That might have been a little corny, honestly, for the opening scene of the show," Peterson said at Comic-Con, per Screener.
Eventually, the mute ice-blue stare of the Night King as he orders his zombie army to battle became the more terrifying of the choices.
FtwehkDSwfm: That's Skroth for "Can the premiere hurry up already?!" (We *crack* ourselves up.)