English

As in the times before The Rupture, English is the common language that most races use to communicate.
In the short time after The Rupture the other races had to use magic to converse with the humans on the New Earth. The fact that humans were and still remain the most common race on New Earth eventually caused the others to learn the language. It eventually became a language that bridged the communication gap between other races as well.  Depending on where you are in the world, there will be subtleties in the language that change. Humans before The Rupture had a variety of traditions and cultures, and these still remain to this day. These different cultures have an impact on the English language in their area. Slang words from other pre-Rupture languages are mixed in, and eventually even the other races pick up on them with extended stays in these areas.