Google uses a very advanced AI in Youtube that translates speech in real time. You can read these translations as subtitles in real time with the speaker talks in the video. It will be better to listen or translate full speach as voice to your prefered language, though, these subtitles helps alot in researching and learning process. In example there are much more contents in English for learning any IT subjects then there is in Turkish. I do not need to learn a English to get my free online youtube course. I can turn on subtitles and from settings > autotanslate, I can choose my prefered language like Turkish. And result, I can take an IT course from Harward University in Turkish. Here, follow the reference images that might help you.