Proofreading is always included in translation and subtitling work - however, you may also hire me for proofreading exclusively to ensure that existing German or English texts are valid and flawless.
The complexity of the proofreading job is determined by the quality delivered by the writer or translator who was originally responsible for the text at hand. In theory, everybody working with written language(s) should be well-versed and firm in orthography, grammar, punctuation, and wording. In practice, this isn't always the case which makes proofreading all the more necessary.
There are times when a source text contains so many errors that correcting them is bound to be a never-ending story. In these cases, translating from scratch will save our time, my nerves, and your money and will be superior in quality by a long shot.