What is the polite thing to do when others don't understand what you are saying? How do other parents resolve it? What can you get away with, and what are some tricks?
Actually, the concern about excluding people from parts of the conversation can play at two levels -- on the micro level at home as well as at the macro level within the larger community.
Let's start at home. Here Cho from Phoenix hits the nail on the head:
"I am Japanese, my husband is Polish, and we live in the US. Our common language is English. We are expecting a baby soon and want to speak our two native languages to him/her. But we don't understand each other's languages, so we are concerned that we will not be able to have meaningful family conversations."
Many multilingual families face this dilemma that has jokingly been dubbed 'RTDTL', meaning 'round-the-dinner-table-languages'. The normal solution is that the parents learn alongside the child. Both parents should consider taking a beginner's course in each other's language to get some of the basics down. Remember that the level of conversation with baby isn't very advanced for the first years, so there is plenty of time for both of you to learn. As your child becomes a more sophisticated talker, you will have to accept that you are not going to understand everything that passes between him and the other parent.
Obviously, when it is important that everyone understand, you can allow yourself the occasional lapse into the community language, but mostly you'll just depend upon simultaneous translation which will become second nature to you very soon -- trust me! The other trick is to talk 'about' the children to the other parent in your common language rather speak 'to' them. Finally, as the child gets older, and speaks both languages well, you can allow more and more community language (or common language, if that is other than the community language) into the conversation. Luckily, the advance in language usually coincides with the desire for more sophisticated family conversations -- somewhere around the age of four or five. Depending how much everyone knows of each other's languages by then, a practical solution has usually already fallen into place.
The other option, if you really don't like the strict 'one person one language' idea, is to always speak your common language when you are all together. But, in that situation, the child may well learn to understand the minority languages, but probably not speak it. Children are very quick to avoid doing things unless they absolutely have to. So once the child figures out that it is okay to speak the community language to the parents, it will probably become the default (the coin drops for them on that somewhere around 2 years old). But, as always, you as a family will have to make a decision that will work for you in your unique situation. In the end everybody will have to feel comfortable with how RTDTL is conducted in your household.
Out and about
Obviously you feel bad when you exclude someone in your own family from parts of a conversation, even if that person has bought into that idea himself or herself. Complete strangers however are more likely to take offense at not understanding what you say to your child. It seems as if overhearing people's conversations is something others consider a right. Or, at the very least, it makes them visibly uneasy not to understand what you are saying -- somewhat akin to you suddenly starting to whisper to your child. The most common reaction from others is to immediately assume you are talking about them. Well, the truth of it is that you'll have to learn to live with some of that. Translate when it is important to you, and just leave it for the rest. We simply can't please everybody all the time.
Conversely, at times you yourself may prefer that strangers understand you -- like when you are telling you child to give back the bucket she just snatched from another child at the playground. A good trick is to translate what you just said to the person concerned, rather than addressing it to your own child. Simply tell the other kid that he'll get his bucket back so that he knows what is going on. This will usually put the other parents at ease as well.
The rule of thumb is rather straightforward in determining the allowances you make for the clerk in the grocery store, the parents on the playground, the teachers at school, etc. It simply depends how important it is that they understand what you and your child are chatting about, weighed against the importance of keeping the language system consistent. This ratio is obviously different for everyone, but you'll soon have a few kind sentences with a positive spin up the sleeve -- because you'll use them often. Here is just one example:
Me, to my daughter at the fish counter (in Swedish). "Look, the crabs are finally in season!" She, whining, as she makes a foul face (in Swedish). "I don't like crabs." The lady behind the counter in English: "May I help you?" while looking questioningly and slightly disapprovingly at my girl. Me, in English: "Your crabs look wonderful to me, but my daughter thinks she doesn't like them. Oh well, all the more for the rest of us!"