The feature was spotted by Android Police on a Google Pixel 5, and you can see the translate button near the bottom of the display and above the screenshot and selector. It seems that the button will appear if something in your recent apps view is set to a language that differs from your phone’s default. When selected, it will apparently enter the app and auto-detect the language to be translated.
The new translate feature appears to be related to what Google announced back in December as part of the Pixel Drop. The update was expected to bring a translate button to the Pixel screenshot function, but it never showed. Perhaps Google decided to hold off to bring Lens to more parts of Android, suggesting there could be deeper Lens AI integration in the works for Android 12. The option still doesn’t appear on screenshots, though, so at this point, it’s anyone’s guess what Google’s plans are.
Android Police notes that their Pixel 5 is on the latest Developer Preview 2.1, although the feature doesn’t appear to be tied to a particular version and could be a server-side update or limited A/B test. We may learn more once Google launches the beta release for Android 12, which is expected in May and will likely be available on more of the best Android phones.