So I've been thinking about the multi-cultural nature of my stories and making decisions about how much of another language, if any, I should include in my narratives and dialogue. Even though English is my primary language, my first words were in Mandarin Chinese.
People who were raised speaking at least two different languages know that there is more than one way to say something. They also know it is possible for a concept or phrase to exist in one language and not another. Such knowledge is extremely useful to writers.
Sometimes in my stories I will include a few uniquely Asian-American circumstances as jokes and play on phrases to those who understand both languages that I'm writing while trying to make it still understandable to the English-only readers. But usually my overall guiding principle in writing is that I should put in non-English language phrases only when absolutely necessary, when there is not an appropriate translation in English.