This paper describes research activities for exploring techniques of cross-language information retrieval (CLIR) during the NACSIS Test Collection for Information Retrieval/NII Testbeds and Community for Information access Research (NTCIR)-1 to NTCIR-6 evaluation cycles, which mainly focused on Chinese, Japanese, and Korean (CJK) languages. First, general procedures and techniques of CLIR are briefly reviewed. Second, document collections that were used for the research tasks and test collection construction for retrieval experiments are explained. Specifically, CLIR tasks from NTCIR-3 to NTCIR-6 utilized multilingual corpora consisting of newspaper articles that were published in Taiwan, Japan, and Korea during the same time periods. A set of articles can be considered a “pseudo” comparable corpus because many events or affairs are commonly covered across languages in the articles. Such comparable corpora are helpful for comparing the performance of CLIR between pairs of CJK and English. This comparison leads to deeper insights into CLIR techniques. NTCIR CLIR tasks have been built on the basis of test collections that incorporate such comparable corpora. We summarize the technical advances observed in these CLIR tasks at the end of the paper.