I do think that I think in specific languages. The language I think in does change during the day for example: if I am working on school work, reading English stories or watching English clips on youtube I am usually thinking in English and have to switch to Dutch again when speaking to my mother. If I am speaking Dutch all day I also think in Dutch.

Thinking does go faster than speaking because there are no muscles involved in thinking only neurons. Neurons work at a speed that cannot be matched by your muscles forming words. It is also important that you think before you speak. You cannot say everything you think, you need to curb some of your thoughts to not offend anyone and to keep making sense. If I said everything I think I would not be able to have a conversation with anyone because I would keep speaking and not listening.