I have two kinds of languages like that.
First, I am used to make up words in French, based on English words. The most famous one in my family makes my brother laugh each time I use it. I say "basicalement", which comes from "basically", but which has no meaning in French.
Also, we have a language on my father's side, with a vocabulary, grammar rules, etc, and we wrote books to learn it. It sounds like Eastern Europe languages with some Spanish and English in it, which is quite funny to hear when you are not used to it. We call it with a name my father and his siblings came up with when they were teenagers : "syriaque". This name has no meaning.
Loy
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Nicolas (spark).