Let me start with a quick disclaimer: Sofia is six months old. She doesn't make any utterances which constitute language yet. I am not one of these misguided parents who eagerly listen to baby's every gurgle and burp and try and translate it into something linguistically meaningful (although if pushed I might admit to having displayed such tendencies with Leonard, the first baby...).
The interesting thing is that if you ask adult speakers of the different languages spoken in Sofia's world, they will all tell you she is speaking their language. A Swiss friend happily burbles to our babies, repeating "areuh" back to them (it's a real French word, check it out on google), whereas any English person talking with them will say "ga ga" and so will baby. For Germans this is a bit more difficult, because there doesn't appear to be a stereotypical baby sound in German. I asked a number of friends what you would see in a cartoon bubble for babytalk and they couldn't come up with anything specific. But anyway, you get the general idea.
So what does this tell us? That all adults speaking to babies are misguided and only hear what they want to hear? Or that Sofia has been reading the comics and knows what she should be saying to whom? One thing is sure (cos science says so): studies have shown that by about the age of 6 months babies have started to filter out the sounds which are not useful to them in the language(s) spoken to them. This is why Japanese native speakers famously cannot hear and often pronounce a distinction between a 'l' and an 'r', because this distinction isn't used in Japanese. It's also why I have great difficulties with 'u' and ' ü' in German. I've learnt to pronounce two different sounds which approximate fairly closely to those used by German native speakers (amongst other things by means of a hilarious exercise involving imitating a frog in front of a mirror, taught to me by a German teacher who was so square that I just had to believe that she wasn't making fun of me). But I still have huge difficulties hearing the difference between the two, to Thomas' great amusement, particularly when it comes to the difference between "drucken" (to print) and "drücken" (to press or squeeze), especially in the idiomatic expression "Ich drücke dich", meaning to give someone a hug, which I invariably mispronounce as "I print you!"
But I digress. Sofia is definitely on her way to being able to distinguish the sounds made in English, German and French and to have the potential to be able to reproduce them. Although something strange happens along the way (or maybe not so strange: see Prof. Grosjean's expert blog). For example, the older multilingual children we know whose schooling is in French speak their other languages with the cutest of little French accents. But it goes away when they leave home to live in an entirely native-speaker environment. And the kids we know who go to the English-language international schools seem to come out with fairly spooky mid-Atlantic accents, mixing and matching pretty random bits of British and American pronounciation and slang.
I shall have to stop. Said baby has just woken up (very unusually) screaming - I'll leave you to ponder in which language.