Offshore software development (OSD) is international business collaboration. OSD projects often encounter intercultural and inter-linguistic problems disturbing the projects. Business documents are formal media of information and knowledge for OSD. While OSD documents should convey common understanding of the OSD products, the documents may contain unsuitable expressions which draw misunderstanding of the required products and offensive issues for the collaboration. Intercultural and inter-linguistic differences cause mistakes and inappropriate expressions. OSD from Japan to China is the largest in Asia, and Japanese language is often used in OSD documents. Large similarity is found between Japanese and Chinese in their languages, while many differences exist even for the same word. The similarity induces to write unsuitable expressions for both sides of OSD. To introduce risks for OSD projects caused by unsuitable or inappropriate expressions in OSD documents, we propose to apply a proofreading system of Japanese documents for OSD. Japanese consignor uses the system to refine OSD documents written by Japanese engineers for Chinese readers, and Chinese consignee uses it to refine Japanese documents written by Chinese Engineers as derivatives of OSD projects. Effectiveness of applying the proofreading system is discussed for actual projects.