Siri translation seems like the most obvious thing in the world. You probably already asked him/her the meaning of a foreign word, or how to say an English phrase in another language. Under iOS 11, though, this will actually work.
All you have to do is to ask Siri how to say something, and s/he will respond with an answer. Even better, you can use Type to Siri to make the query, which may come in handy when you’re in a line at the market and you don’t want to start talking into your iPhone.