How an author deals with translated plagiarism: A case study

Case: An author published a case report for a rare disease in a Japanese journal 10 years ago. A few years later, he published a comparison of two cases in an international English language journal. One of the cases was the same as the one published in the Japanese paper. The English paper included translated material from the Japanese paper, without a citation to the original. It has been five years since the English paper was published.