To say "let's go play" in Engpsh, you can say "let's go have some fun" or "let's go play around." You can also simply say "let's go play" or "let's go have a good time." If you want to be more specific about what you will be doing, you can say something pke "let's go play a game," "let's go have a picnic," or "let's go go for a hike."