It's a neat and potentially very useful trick, and the feature is now live for anyone to use so long as they have a Google Home or Google Smart Display. Some third-party Google Assistant speakers also support the Interpreter, but not all of them, so you'll need to check yours is compatible.
There are 26 languages supported at launch, and as the name suggests, you can use the Google Assistant Interpreter to translate a conversation between yourself and another person.
One thing to know right away: while there are 26 languages supported in total, you must use English, French, German, Italian, Japanese, or Spanish to launch the Interpreter, at which point you can then start translating the other languages.
The full 26 include: Czech, Danish, Dutch, English, Finnish, French, German, Greek, Hindi, Hungarian, Indonesian, Italian, Japanese, Korean, Mandarin, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, Swedish, Thai, Turkish, Ukrainian, and Vietnamese.
How to start translating a conversation
Ready to start translating? Here's what you need to do.
1. Say, "Ok/Hey Google"
2. Say something like "Help me speak Italian", "Be my Spanish interpreter" or "Translate Japanese to Hungarian". You can also just say, "Turn on Interpreter mode". Pro tip: Saying "Speak Spanish", "Can you speak Italian?" and "Translate [language]" won't work.
3. If you've already told Google the languages you want to translate you'll need to now do so.
4. Wait for the tone, then start speaking in one of the two languages.
Handily, you don't have to alternate between the two languages, however you do have to wait for the Google Assistant to process, which can take a few seconds. So patience is key.
To stop using the Interpreter, simply say "Off", "Exit" or "Quit".
If you're using a Google Smart Display like a Google Home Hub, you'll get the added benefit of being able to see the words on the screen before and after they're translated. Another thing to know if you're using a Smart Display: you can dismiss the Interpreter with a simple left swipe on the screen, or one of the aforementioned commands.
And that's it. Happy translating.