When you learn a new language you gain more than the ability to communicate with people from a different place. Languages do not overlap 1 to 1, each word on one side corresponding to one on the other. They stack on top of each other irregularly, leaving you with a larger vocabulary made of new words and new idioms. Your sensorial surface grows, you can feel new things.
Families speaking multiple languages at once often seems to be mixing them regularly. We do it all the time. It is not a symptom of confusion, of incomplete knowledge. It is the advantage of pulling from multiple sources to convey a message. Each language has a number of critical expressions that you don't find in the other. They exist in your mind, in your perception, but you can't truly feel them before you learn that new word.
I read this paragraph last night:
"Perhaps a writer would think of the monosyllables and lack of grammatical inflection in Chinese, and of how this would sound next to lovely long Finnish words all double letters & long vowels in 14 cases or lovely Hungarian all prefixes suffixes, & having first thought of that would then think of some story about Hungarians or Finns with Chinese."*
That's how my life often feels. That's also what life at Founders office feels.
Languages are also more than words. Danish, for example, is extremely phonetical. Every person who has tried to learn it has felt the pain of having more knowledge in our head than what we can get understood. You think you know that word, but they keep not getting what you are trying to say. It frustrated the hell out of me. Couldn't they at least try?! Truth is they just don't understand what you say. Mispronounced words are non-words.
It's interesting how this affects how the language itself is thought to young children. My daughter has just started school and she learning to read. But you can't read Danish as you would read Italian, stringing together the sounds of each letter into a full word. You need to know what an entire word sounds like before you can read it. You need to spot it on the page, recollect what word it is (by it signs) and then say it as it is pronounced, in one go. The way to do it is to start with very short words. So she comes home with these short books written entirely with two-letter words. It is a funny constraint if you think about it. How does the writer come up with a story written only combining two-letter words? That's when you get a cow (kø) drinking beer (øl). Creativity is also about that.
* In "The last samurai", by Helen DeWitt