Other languages

My Mom sometimes spoke to friends in Japanese, possibly because they were more comfortable in that language and perhaps also so my brothers and I would not understand. We mostly spoke English at home, but my Mom would also use Japanese when she got mad at us. Later, I learned how to speak some and lived in Japan. But now I don’t any more. I have been writing a story about characters who speak Japanese. I wonder about when to use Japanese words and whether or not to translate them and the different effects that produces depending on the reader.