It is good to add subtitles by first correcting the auto-generated subtitles. Once this is done.. add all the languages possible. I guess Tubebuddy has a limit of 24 languages for Legend members because I have a legend account and after adding 24 languages in a day, I got a message to wait for 24 hours. Anyways, as per YouTube in their guidelines and one of their videos, it says, adding subtitles can increase the views in countries where the default language of your video is not spoken. Also, adding subtitles, increases watch time.