Wow, just learned from the post about OPOL [0], didn't know it was a thing, but at least in our case it worked for 3 languages. My wife and I speak different languages (French and Spanish), we each speak exclusively with that one to our kids. They didn't know English when they started preschool, but it took them a couple of months. Right now they are close to native on all 3. Kids are amazing
We did the same but with German/Swedish/English. Kid learns american english from youtube and movies and the main language in Swedish schools is English anyway... The Swedish teachers are complaining quitely that the youth talk more English than Swedish the last 10 years.
[0] https://smartparentingpod.com/one-parent-one-language-opol-m...