My kid and I sometimes speak to in each other in a mix of three languages, and neither of us really notices when the other changes language mid-sentence. Doing the same with a friend I started hanging out with, with the same languages. I've noticed that I find it easier to speak about psychological things in English, and about gardening in Portuguese - that for each to pic I have my preferred language, but will throw in whatever word I cannot remember in another language. It's faster to communicate like that with my friends and family than religiously sticking to only one language.