When you're multilingual, you'd switch between languages on the fly, mid-sentence even, just because the words in other language come to your mind quicker, seem to better match nuances, etc.
Btw, I cannot recommend enough the other work by Marcin Wichary. For me, he's the paragon of making the most of what you can do in terms of, to put it best, tailoring things exactly to your specific needs and tastes. (My copy of Shift Happens is on its way, can't wait!)