If you've ever made up a language just to communicate specially between you and your folks,raise your hands! I have and it's funny how we understand ourselves so well!!!
There was a special way to talk when I was a kid like replacing all the vocals for an specific one like i, but per se created a language, never.
A sign language and a written language (it contained numbers as letters, so we couldn't actually speak it)
I created a topic once that included that
Feel free to comment if you have anything to say
In childhood, we had this language where you add "p" and the vowel used just before that, after each syllable. We called it the Parrot language, or parrotting. For example:
I didn't have lunch today.
You would say:
I-pa di-pi dnt he-pev la-panch to-po da-pay.
I just transliterated it in English for the first time, and you use the same sounding/vowels as without it, but we did this in Macedonian, my mother tongue, and given there are no reading rules in it, you read how you write, it was a bit easier. But I was myself very good in it, very quick and I loved transforming the words in that form quickly and bold. I am glad I am recalling it now. Otherwise, everyone knew this language, so it wasn't any secret language, but with specific friends, we always had some sort of signs/symbols to understand each other among people not as close to us. But we never invented a whole or partial language with vocabulary and all.
That is so great! There was something similar we used to do in highschool too, but with my siblings,we just said random words that started making sense to us over time. There was no precision to it,and our 'special language' wasn't very broad,just a few words if we wanted to keep our parents out of the loop,lol.