The most commonly spoken language in inhabited space is Franca, the language of the Earth Empire and its offshoot Civs. All humans speak it, even though many worlds and regions of worlds also have their own languages and dialects, and all NOIs of the Distributed Process are capable of communicating in it as well. It's a post-creole made largely from a fairly even mix of French, Hindi, Mandarin, heavily seasoned with English and Japanese and a pinch of Spanish.
The Many are unable to form a significant proportion of the sounds needed to speak Franca, but this is not a great impediment to communication, as they habitually carry or wear translation devices to offset the rapid evolution of their own myriad languages. Carried as handheld devices or worn as pendants or headgear, they vary from smooth, fast expensive models that sound like native speakers, to cheap travesties of electronics that sound like a speak and spell gargling boiling sandpaper at 5 seconds a word.
The Zebulon have their own set of languages, of course, but also possess a capacity for language learning that makes non Franca speakers rare in their society, especially among those who have business offworld. Some Zebulon find it intellectually justifiable or simply amusing to show the inefficiency of Franca by using as few words as possible when talking to Humans, or even to pretend not to speak or understand it well. Others act like they're beating their interlocutors around the ears with a thesaurus.
Franca will be physrepped in-game with English.