Standard language in human space. English. For the most part similar to today, even despite other languages changing, to different extents. There is a reason for this. See, way back in the mid-22nd century, people realized that the language would rapidly shift and, in even less than a thousand years, become nearly unintelligible to each other. That's, obviously, quite the problem. So the idea that English, the lingua franca, should be kept the same as today really took off fast. Some government involvment and so on, and nowadays that idea is very popular, and perhaps the only thing truly universal to human space.
Human space. Similar to modern day, the language has remained the lingua franca of the human world. As most colonies have their own languages, due to originating from different places, a standard language for conversation between people had to exist. Conveniently, english has been a common language on Earth for a while. So, due to this, and the fact that most people know english, it became galactic standard language.