title_body: From known languages, what are the expected features of a Generation Ship Language?
upvoted_answer: The idea that language would not change over 1000 years of travel in space is absolutely ludicrous. 1000 years ago was before Middle English existed. Massive amounts of language change can occur over such a long period of time. Even very conservative languages change significantly over such a long period of time. No language will remain unchanged after 1000 years. Based on natlangs, it's more likely than not that the language will not be mutually intelligible with its predecessor after 1000 years.
  
  How exactly the language changes depends a lot on the details of the situation -- how multicultural is the ship? What is the lingua franca of the ship? How are other languages viewed relative to the lingua franca? If there is enough of a divide in where different languages are used (such as if everything for official purposes is in English but a great number of native, say, Spanish speakers speak Spanish with their families at home), you may end up with diglossia arising. If there are significant numbers of multilingual people on these ships, you can bet there will be a lot of borrowing from minority languages into the dominant language, at least in less formal contexts. As in real life, there may be stigma against using such borrowings.
  
  Honestly, language change in this situation won't likely differ that much from language change anywhere else. A conlanger has a lot of freedom in how they want to deal with the diachronics in this situation. The only real difference is that you don't have any chance of outsiders suddenly arriving and bringing with them waves of loanwords. ...Well, at least, you probably don't.