An interpreter is in fact provided for important communications, but it's a given that there's not going to be interpreters on-hand for every foreign prisoner 24/7. I think most people would simply accept that a language barrier is a normal fact of life of being arrested in a foreign country. The expectation of not needing to speak a foreign language in a foreign country seems to be a uniquely English one, and it manifests in other ways. There are many people who come to Japan to teach English without understanding a word of Japanese, and then complain about the difficulty of life, how restaraunt staff won't speak English or provide an English menu for them, how this and that are not provided for in English. They don't attempt to learn Japanese even after teaching for 5+ years, and yet criticise Japan for not catering to their needs. The sense of entitlement gets nauseating after you've witnessed it enough.