Most of my proofing work was grammar- or layout-related. Choice of words, where best to put a sentence and how best to say it. Since it was a translation project from Japanese to English, it look a little massaging here and there to fully convey meanings for words and phrases that don't exactly carry over into English idiom. Primarily, we focused on the most direct and accurate translation possible. Following that, we would read over the full text and determine if anything was too esoteric and, if so, tried to rephrase it in a way that kept the meaning clear without cluttering up the translation. All in all, it was a very interesting exercise. I've been at it for over 5 years and my expertise is in the English side of things.