Have you ever noticed that sibling toddlers converse with one another in what I call their 'mother tongue'. They can understand one another, and only they can understand one another.
If you were one of these siblings and wish to revisit your mother tongue, take it from me, about ten shots of tequila ought to do it.
When I got married twenty years ago my father advised me to keep a journal of the things which were important to my wife.
I did this and boy has it come in handy. Just the other day she asked, "How many times do I need to tell you that?"
I looked it up and sure enough 14 years ago she casually mentioned it to me. I'm advising my son to memorize his journal.