Lingo

Each settlement has its own language, or "lingo".
They are all a mix of different languages spoken by the Ancients, although most of them are heavily distorted variations of Ancient English, with a lot of words and grammatics borrowed mainly from Spanish and Chinese, but also from Punjabi, German, Filipino, French, Korean, Farsi, Vietnamese, Arabic, Russian, and many others.
Most settlements still use variations of the alphabet used by the Ancients, while others developed their own codified writing to keep their messages secret, and the codes ended up being used as their alphabet.
In most cases, if people talk slowly and use gestures, they can understand at least half of what a foreigner is trying to say.