According to Android Police, the trial is triggered server side for the few who have been selected for it. So if you don’t see it, then no number of updates for the YouTube app will make it appear. And it’s especially if your native language is not Portuguese. At the moment, that seems to be only language that video platform automatically translates to.
But when the translation is seen in action, it translates nearly everything. UI items like the Home, Explore, Subscriptions and Library buttons go without saying. But amazingly, video titles and descriptions are translated, as well as closed captions while the video is playing. Though it’s easy to see this go a little wrong sometimes, since the automatic captioning is not perfect. Neither YouTube nor parent company Google has said anything on an official capacity regarding this test just yet. Hopefully it gets expanded to other languages as well. After all, Google Translate works with over 100 languages, not to mention its other non-text translation capabilities. And with both services being under the same Google umbrella, it’s not an unfair expectation to have. (Source: Android Police)
