You think primarily in your native language. You will seamlessly think in your second or third language when it better conveys an idea. Much the way you'd slip into a second or third language in conversation to get a subtext or non-literal across. This is particularly the case for idioms or inside jokes. E.g. "Porque no los dos?" literally means "why not the two?", but idiomatically conveys choosing between two (usually unwise or bad) ideas and smacking BOTH buttons at once for the lulz. E.g. "Should we do tequila shots or streak through the neighborhood" would beg for a response of porque no los dos to point out how bad an idea either is. As an alternate example, if I'm cajoling my spouse, the goto thought or phrase always starts with mon cheri in an outrageous French accent. I wouldnt even think of that in English because it's a stodgy language to convey over the top flattery.