I am working with an international client who is writing a manuscript in English, his second language. While I can freely edit his parts of the text, it becomes thornier when he uses (incorrect) excerpts from other authors who are second language writers. I first mentioned to him the use of [sic], but this could get repetitive in some (non-native) texts that are as long as a paragraph. I liked Avrom's suggestion. It allows the full manuscript to read cleanly while only slightly calling attention to the error(s). Thanks, all. Great discussion!