Some translation plugins allow you to make automatic translations available for search engines to index.
These machine translations are not very good. They can be odd and even misleading at times. Allowing search engines to index this low-quality content is a bad idea. Google can identify this content and will consider it spam, which would damage your website’s search rankings.
However, for manual site translations, you should let Google index your translated versions, so you can rank higher in local SEO.