Our toddler is raised in a multilingual environment. I speak only one natively. However, I find awkward and unnatural to speak just one language to him from the argument that this will confuse him.
Being multilingual is not only about the acquisition of the language but also learning the ability to switch and handle different languages... No way to find a research paper or experience, so perhaps more luck here...
I have a friend who is doing a PhD in bilingualism, who claims that speaking more than one language will in fact not confuse a child in any linguistic sense. However, how well the child learns each language is directly related to how much he/she is exposed to it. If you are the only source of your language to your child, speaking less in that language is probably not the best idea.
My own experience with different languages is that I switch effortlessly between the two that I know well, while it's a whole process to switch to one of the two that I'm not really fluent in. This is especially true of the one I learned in my thirties. It takes a good ten minutes to not strain enormously the whole time. So again, it is probably the best thing to do whatever it takes to make your child learn each language well, and in this case that means speaking just one language.
I am going to have a similar situation as you when my son gets a bit older. The advice we got (not from the linguist - from a pediatric nurse) was to use the language of the country we live in when he has friends over, but to use our own language(s) in all other situations. This seemed reasonable to me.
I think the point of the one language per person rule is to make the child learn to be consistent with the languages in question. (S)he needs to learn properly to use each language exclusively when the situation requires that - instead of speaking sentences where half the words come from language A and the other half from language B, or words from language A are used with the grammar of language B.
Children's brains are very flexible, so once they learn two (or more) languages properly, they will have no problem whatsoever switching between them. However, they need to understand the need to switch, depending on whom they are talking to. And I believe the above rule helps them a lot in this.
I remember vividly a scene when our elder daughter was about 15 months old. We were sitting at the dinner table with her, my wife on one side and me on the other, telling her words first in Finnish, then the corresponding word in Hungarian (or vice versa). She was watching us and listening intently, and you could almost hear the cogwheels turning in her head... and then, after a few minutes, we saw a big "a-ha" smile and it was obvious that she got the concept that we are speaking in two different languages! From then on, her language development took to a new level.
I speak four languages fluently and can switch between them in a blink of an eye. I learned them all in my early childhood. I believe that knowing more languages has no negative effects except if the social circle deems it somehow elitist. My wife also speaks several languages. Even so, we have limited our use of language towards our 2-year-old son to one language per person.
My wife speaks only German with him, and I speak only Danish with him. He hears me speak both Danish and German with other people. Because we live in Austria, there are exceptions when I speak German instead of Danish, but only when others need to understand what I'm telling my son.
I could speak three or four languages with my son, but I choose only one in the early years so that he can learn that one well (he will learn another from my wife). I think I would confuse him if I constantly switched language without context or reason.
Context
I'm no expert on this but I would hesitate to use any particular weekday as context for an "English day." My reasoning is that small kids have no concept of "weekdays" so they don't see any context even when you know that the context is "weekend".
If you really want to do this, then perhaps you could connect it to something that small kids understand, like "English after sundown" or "English at the playground."
Third language
This bilingual upbringing is easy for us because the country we live in doesn't involve a third language (e.g. if we lived in England). But I believe that good English skills are immensely important in our international society, so I will add English to the mix in a year or two, or definitely when school starts, but I'm not sure yet how to approach this (stay tuned on this site!).
Also, all our computers have only English software because I prefer it that way. This is not an "educational decision" but will support the learning of English when the time comes.
NO. absolutely not. Please, introduce your child to all of your languages. It will not, by any means, confuse your child. I would suggest that you not use Spanglish, or some other similar thing where you are using multiple languages at the same time, nor would I suggest One language for bed time and another for wake-up time. The more exposure to each language your child gets, the more of an advantage he will have later on (in more ways than you might imagine too - it isn't just about language skills but even how they think. The more languages the more thinking pathways for creativity and problem solving as well).
I would suggest reading, "The Bilingual Edge" to help you figure out all the specifics. The idea of having specific days for specific languages, like Wednesday Welch and Friday French, might not be bad to help you make sure you are using all at your disposal, but might also be too formal and limiting for you too.
