If you have a YouTube Premium subscription, you can try out instant comment translations on Android and iOS. The option is available through YouTube Experiments, but you need to opt in to access it. Once you do, there will be a Translate toggle within the video comment section. The app will then automatically translate any comment that isn't your preset device or app setting. You have a See Original option to get a look at the original comment.
We can't speak for how accurate the translations will be, though. But you can offer feedback if you want through a dedicated questionnaire. This feature will only be live until September 9. We don't yet if YouTube plans to roll this out to more users in the future.
Source: 9to5Google