[Jprogramming] Words formation

[JC Coez]

I would like to use ;: verb to replace special strings by others in a text. 
In other words, I have a text (in french) and a catalog of words (letters 
and possibly special caracters including space) and their corresponding 
substitutes. If there are multiple spaces in the original text, I want to 
keep them too in the result. I thought that the x;:y as explained in the 
dictionary would be the best approach to solve that problem. But I am 
surely missing something and I can't do it.
Are there any some examples of ;:  available somewhere ?
Thanks for any help
JC Coez