Wordy

Your vocabulary is improving surely. Your favourite word for a while now has been "down". I taught you it so you could vocalise your desire to be lowered from my embrace (I was saying "up" too, when I lifted you, but you have trouble with words that begin with certain vowels). You use "down" now to indicate pretty much every desire. If you've had enough to eat and want to get down out of the high chair, it's "down". If you are trying to climb into your cot to play (a recent preference), it's also "down". Lying flat on your back when I change your nappy, "down" means "let me get up".
Your Mandarin vocabulary is also coming on. You have been drawn by barely visible planes from the window for several weeks and now have an approximation of the word. We got a new washing machine yesterday and that having been one of your favourite pictures for a short while in the Picthall and Gunzi's "first Chinese words" book I bought for you last Xmas, you have been excitedly pointing and saying "xiyiji" eveery minute or so at times.
Since we employed Alicia as your first Spanish friend/tutor, you also like saying "si" and you understand and attempt "dame manos". 
Obviously your passive vocabulary is far greater than your active one, and those words you say don't always sound like the word you're expressing but we know what you are saying, son.
Some English words you know:
baby, cat, rainbow, bunny, daddy, mummy, ball, pepper, potato, down, tea

Multilingual

Your mum and I had a chat about languages tonight. We've both heard that if one person does not consistently speak a single language (ie if I speak to you in English, Spanish and Japanese) you will confuse them all. I've always thought this was a myth and that's exactly what multilingualchildren.org says. As long as you get enough language input, you should be able to pick up 3 or 4 languages and it is better to teach them all together rather than wait and do one after the other.

We agreed we would make sure there were enough books in Spanish and Japanese for you and also that we would only let you watch certain films (animation for kids) in languages other than English (Mandarin, too, of course). In the meantime, I decided I need to step up my own language study as both need polishing up. We'll encourage you to learn other languages at school, too.