What language do you think and dream in?

Not sure of the figures (ha, pun! -- to come), but a Chinese friend once observed that no matter how fluent one might be in a foreign language, one always reverts to one's original language when needing to involve numbers aloud (e.g., doing mental sums).  


My mobile was given to me by a Chinese friend who was upgrading (and wanted me to be on call to help her with interpreting in emergencies), so my first acquaintance with the phone number was in Chinese.  Since then, whenever people ask me for my phone number, I'll say it in Chinese first (and convert it into English if the listener can't understand Chinese).  It's like a tune in my head.


I often ask people what language they dream in.  I think it's a sign of one's mastery of a foreign language if one starts thinking and dreaming in that language.  What happens when one's a polyglot, I wonder?  Multi-lingual thoughts and dreams?  I know that Singaporeans do that in their everyday life, mixing English, Chinese and Malay in the same sentence.  An ex-student, Philip, who's been relocated to Singapore, says he can barely understand what the locals say because of this element, for one thing.  Ordering a coffee is such a linguistic minefield that he ends up just taking whatever they give him, poor man (but it makes me chuckle, imagining his total bafflement just trying to get a coffee).