Trying to build a simple Letter Scrambler

I am looking to build a very simple letter scrambler.

I want to build two boxes for text just like a translation tool. The first box is for whatever text that you want to insert and the second box will be for the translation.

The scrambler will translate each individual letter/character into a different character from a random list for each individual letter. "A" will randomly turn into "À","Á","Â","Ã","Ä","Å","Ā","Ă","Ą","Α","Å" or "𝔸" in the translation. and so forth for all the upper and lowercase letters.

This tutorial https://www.youtube.com/watch?v=RVKDWPXdWiw shows kind of what I am trying to build but I just want it to go to the lists of random letters rather than the picture files.

Can someone explain the code to do that in php or some other program language?