I think Scot Gimple has said that The Scavengers talk that way out of purpose because they've, out a form of necessity, simplified and truncated their manner of speaking for efficiency and to allow them to communicate in a manner less likely to draw in walkers or otherwise unwanted intention.
So they're talking that way intentionally by design and choice and three years may just be enough time for it to set in and become just the way they talk. A friend of mine spent two years on a mission in Bolivia as per tradition/implied requirement/non-requirement in the LDS chuch. For those two years he mostly spoke Spanish in the Spanish-speaking country and when he returned he had a noticeable (Bolivian) accent and struggled to find the words in English he wanted when talking. Spending two years speaking Spanish had damaged, to a degree, his ability to speak English. Now, he was back on his feet and speaking clear English without being at a loss for words and without an accent in a fairly short amount of time, a couple weeks, but it suggests it is possible if you communicate in a different way for at least 2 years it becomes just the way you talk.
The ZA has been going on for the greater part of 3 years, we may be able to argue for almost 4 considering how Judith now looks, and if The Scavengers are anything like the Alexandrians they've probably been together and isolated pretty much since the beginning. So, as ridiculous as it may seem it's "possible" for them to have simply rebuilt the way they talk out of some form of necessity or efficiency and have been doing it long enough and consistently enough it's neutered their regular way of speaking.
Like my friend, they could probably undo this programming pretty quickly if they began speaking regularly again, but for them this way of talking works for their purposes. Think about it, with hand signals, a nod and a flare, not having to speak a word, Jadis was able to get her lieutenant to signal the others to lay out a smoke-screen and to cut and run.
Rick's group didn't even have a plan to regroup somewhere should something drastic happen at the prison and all of the characters wandered and stumbled around for several days before reuniting at Terminus. Granted, stupidity on their part for not having some form of contingency organized for at least the core group to meet somewhere in an emergency, but it still wouldn't have been easy or effective to tell everyone, with a short signal, "abandon the plan, meet at the place." Jadis was able to get her group to do this with a couple signals.
Very efficient. They are Jadis.
