I also agree that “each parent speaks one language” is best when one parent is strong in one language, and the other parent is strong in the other.
But in practice, the rule breaks down over time (for us). My wife’s spoken Chinese is stronger than mine (I speak with an American accent), but my reading is better. For years, my wife hated it when I read to my kids in Chinese. She was afraid that I’d pass down my American accent.
But when my wife could no longer work through our kids’ Chinese textbooks, I took over homework help for that subject.
At the dinner table, I speak English and my wife speaks half English and half Chinese (my wife has a native Chinese accent, but she uses English when she doesn’t know the Chinese word for what she wants to say). My kids speak English to me, (mostly) Chinese to my wife, and half-and-half when we’re conversing as a family and their words aren’t directed at any particular person.
Our household is biased toward English… which isn’t a problem because they get plenty of Chinese outside the house. We used to be strictly half-English and half-Chinese at home, but our kids were becoming too strong in Chinese and their English was falling behind. So, we slanted our household conversation to become more English-oriented (I’m English and my wife is half-and-half). Honestly, this feels more natural, and our kids’ English has improved.
But when it comes to books and homework, (and reading as a family) the REAL hodgepodge of languages sets in.
I’ll help my son work through the Chinese text, but he has learned to ask me questions about the passage in English because I’m the English speaker during casual conversation. I’ll explain in English, which is basically translating it. When we read books as a family in either language, I’m the designated reader.
Memorizing Chinese passages is a bit of a struggle. I’m the one who drills my kids (sometimes my wife doesn’t know the characters) but my wife has the final say about whether my son is pronuncing it correctly. My daughter hates memorizing, so my wife isn’t strict about her pronunciation because we’re happy as long as she does her homework.
When we work on passages above our kids’ grade levels, they’re welcome to translate the passages into English instead of reciting them verbatim in Chinese. This is easier for them because they’re allowed to transate the passages slightly differently each time (not as strict). I’m not sure what my son’s teachers will think when he gets to that level in a few years.
As for what system to put into place… just do what comes natural (as long as “natural” involves both languages in some form!)
We tried adhering to strict rules in the past, but I’ve found that if it doesn’t come naturally, you won’t stick to it for the long haul.
Figure it out as you go along. Constantly re-evaluate. You will run into problems, but you’ll know whether you’re on the right track by listening to your kids speak. If your kids aren’t as strong in one language as you’d hope, restructure your plan and move forward.