A new report just released by a linguistics professor from the University of Michigan questions whether space colonists would be able to communicate with their Earth-bound forefathers in as little as 200 years. Her theory explains that, even if the colonists shared the most common Earth-based language (she suggests English), that many words would simply fade out of existence, for example: airplane, car, train, and skyscraper.
And, even if the language did not mutate dramatically, her report shows plenty of precedent for colonists developing a completely distinct vernacular. Ex: The British and the Americans.