How many reviews do I need from community to make my submitted subtitles to appear on others YouTube videos?
Your content needs to be approved by the video owner.
As mentioned on Google support:
Some channels let you contribute titles, descriptions, subtitles and closed captions to their videos. They're viewable on the video watch page and by clicking the [CC] icon in the player. Approved content is controlled by the video owner, but you can get credit for your contributions on the video.