title_body: "Turing-completeness" in conlangs Programming languages &amp; programs are often said to be Turing complete when it's possible to simulate any Turing machine with it. 
  
  I'm now designing a constructed language for my game and I want everything to be possible to say in it. How can I know if the language is "Turing complete", that  is possible to say/describe everything using it? What would be the requirements for it? What words does the language need to have to be able to speak in it?
  
  For now, everything I thought about:
  
  
  It's possible to describe the past, the present and the future (ex. "I bought a car", "I'm buying a car", "I will buy a car")
  It's possible to describe something (words?) (ex. "The cat is red")
  It's possible to describe nearby area/terrain (ex. "There is a tree")
  It's possible to describe plans (ex. "I want to buy a car")
  Any more ideas?
upvoted_answer: The best parallel for Turing completeness in human languages is the Natural Semantic Metalanguage. The NSM proposes that there is a limited set of basic semantic concepts which all human languages have, and which are not reducible to other concepts. They call these "semantic primes", because you combine them to get all other meanings, and because they can't be broken down. The list of primes, currently numbering 65, is a work in progress as new primes are proposed and evaluated, but after over 45 years of work on the theory the list has proven to be very reliable and new primes are only rarely proposed.
  
  The NSM is a good guide therefore for judging whether a conlang is "complete" - whether it would be as capable for expressing human thought as any natural language. If a conlang has vocabulary items (they can be words, affixes, or phrases) for each of the semantic primes then I would judge it to be complete.