How to create your own language (layout)?

Question

Character encoding

My friend and I came up with symbols with which we replace letters. That is (a square with a dot in the middle) is the letter "N" and thus we encrypt letters and whole sentences. But it turns out only in reality on a piece of paper. And it is possible to create your own characters and add them as a whole language / layout on the computer. So I found in the computer "Installing / Removing interface languages" and there you need to specify the path to the language. So it is possible to create your own symbols and set their layout, but how?