Jürgen Habermas, who popularized the concept of the “post-secular,” advocates that all citizens should be free to decide whether they want to use religious language in the public sphere. However, he adds the proviso that citizens who do so must accept that religious utterances ought to be translated into generally accessible language. Habermas presents this concept of “translation”—or the institutional translation proviso—as a way of bringing religious citizens into the public sphere. In his opinion, the public sphere and/or public institutions should not be open to any movement that tries to legitimize the nation on religious grounds. This paper shows that we can find logic and rhetoric that correspond to Habermas’s proviso in courtroom arguments over religion in Japan after World War II. By surveying these disputes, this paper examines whether or not the intended aims of the institutional translation proviso are achieved.