Proofreading is the pre-publishing process of examining the digital collateral to be published for any kind of errors in text or art. Proofreaders are needed to be 100% accurate by default because they are the one to assure the last stage of typographic production before publication.
In un-vetted translation there are chances for grammatical, typo, misconception errors. Since, proof reading in local languages are done by native linguists only. The native linguist has to thoroughly examine these against the source document. Again, in the workflow of proof reading, they have to record all the changes they make to the original translation by using any trackers and inform translators all these.