YouTube now has the ability to listen to Japanese-language YouTube videos narrated/spoken in a computer-generated English voice, as well as listening to the original Japanese. For this explanation, I have chosen a tour video of Tokyo's Asakusa area as an example.
h ttps://www.youtube.com/watch?v=3oKIYTu9rls
(I have placed a space between the h and t in the URL so you can see the URL. You can also view the video at the end of this post.)
This feature works when you view the video from within this thread, as well as viewing it on directly on YouTube. (But when you watch it from within this thread, you must first press the Play button in order to have the cog wheel appear.)
Hover your mouse over the video > In the lower right corner, a cog wheel icon appears. Click on the cog wheel icon. > a Pop-up menu appears. The first choice is Audio Track. It may say English, Japanese, or another language. (But it seems that, at this time, English and Japanese are the only two choices.) > Click on English. The video now plays with a computer-generated voice translating the narration into English.
Changing it back to a Japanese narration
Repeat the previous steps: Hover your mouse over the video > In the lower right corner, a cog wheel icon appears. Click on the cog wheel icon. > a Pop-up menu appears. > Click on Japanese. You can now hear the original narration in Japanese.
It seems that a lot of Japanese-language videos do not support this feature yet. Try this on several Japanese-language videos and see which videos will let you listen in English.
It also seems this feature does not work on videos called Shorts.