Grew up with immigrant parents where Mandarin was spoken in the household but lived in a area with no other Chinese-Americans. Even though I was exposed to the spoken language daily, I wound up forgetting how to read and write Mandarin by middle school.

Did my best to re-learn it but I rarely ever read/write in Mandarin so I would just regress after a bit - by this point I think I’ve re-learned how to read or write basic Mandarin at least three times and have regressed each successive time. Interesting note is that I seem to be significantly faster at re-learning things each time I go back to it, but that might just be constant repetition more than anything.

This is the phenomenon exploited by spaced repetition learning. “Trying to remember” is when you learn things the best.

Reading something in Mandarin for a couple of minutes every few days will be better than weeks of effort every few years, even though it's less time spent overall.