I've never tried to trick it with questions about Modern English grammar but I've asked it about Old English and it gave me words that meant something else entirely. It would be the equivalent of saying how do you say "I am a warrior" in English and it saying "I am a building". The thing is, it is trained on the internet and it doesn't really know what is real and what is fake, what is real language and what is a dialect or slang, or being used incorrectly. It's no different than the Google algorithm that pulls up random Reddit or Quora articles when you ask a question. It's right often enough for you to think it's reliable but it's not. If it's wrong 10% of the time, that's a lot. Now I'm not saying that it's going to be as bad with English as a dead language like Old English, but it's not trained on just academic materials, it's learned everything, even incorporating joke posts into its knowledge.