I've used this service when I was in Asia. You don't need headphones, you can just use your phone via the Google Translate app. Place your phone down within speaking distance of both or all participants, then speak. It will translate and reply back and then allow the other person to speak, repeating the process. It worked extremely well even several years ago so I assume it's gotten better since then.
I was in Asia a few months ago and can confirm, it worked like a charm. I was able to have a long and enjoyable conversation with my cab driver during the full 40-minute ride. By the end, I almost forgot we were speaking to each other through translations. It's hard to say what mistakes it made, but there were never any moments of real misunderstanding. It was the first time I'd used it at length and I was pretty blown away.
