One of my kids began life with a Cajun-French speaking nanny then transitioned to standard French k-8 French immersion schools. She is academically bilingual and after having spent a year of university study in Paris thinks in both languages. 30-40 years ago I was bilingual spanish/english. My spanish command is now at a pre-k level and it sucks. One of the things I hope to do post-retirement is go to a spanish immersion program in Costa Rica. Then maybe an Arabic immersion in Morocco. Both programs are well regarded by gov & industry for teaching execs enough language to function.