When security becomes an issue, so does communication. Whether is is 10 codes or words that mean something to the security, using something to be discreet has always been a part of security. In Iraq, we used words and phrases meaning something else, and police used to use 10 codes.
The reason for some kind of code or even a separate language is to be able to discuss things in front of the perpetrators while not allowing them to understand what is being discussed. This way you keep an eyes on and allow your security staff to be in the loop.
One major thing I would suggest is to become proficient in whatever code or language you are going to use. Make the decision, and learn. I am assuming that the odds of somebody already taking the lead is slim to none. This will be important, along with finding a partner to study with and speak back and forth to.
When selecting a language, if you decide to go that route, find one fairly simple yet uncommon. Spanish would not be ideal since it is the second most widely spoken language in the U.S. I have picked my language I will be studying. Let me put it this way. I took 3 years of spanish in high school, 4 semesters of Arabic in college, and dabbled a little bit in french. I am no expert, heck I barely remember most of what I learned.
This is the big problem. Without use, language skills are lost. As with any skill, practice is a big part of it. While having a buddy will make this easier, as you will have somebody to practice off of, however, having a group studying will make it easier to practice while utilizing other skills you need. This will also get you to find what unique vocabulary you may need to learn for what you are experiencing in your training.
My suggestion is to talk among your survival group or even your friends, as they will probably be your survival group, at least at the start. Find something you find interesting, and go with it. This could be another skill that could save your life, or someone you love. After all, is that not why we do this in the end?