I created a secret language with a friend.
It started off as a code where you rearrange letters and numbers in an order that is directed by symbols. Then we turned it into spoken, by brown townyzing the words we used most and coming up with a new word. We have 98+ words now, after a year of developing. And we can speak it naturally. If I was going to ask you how your day was:
"Lel rard yol penny dit?"
If I wanted to tell you I thought you were a slut when we went to dinner.
"0 vich yol rard 1 maury quib mol cardo ot jellyroll mit."
Replacing English words with other English words when making a secret language will not work, just so you know.