Forth and Prolog are diverse. Ruby and Java are not. They are both algol (C) derived syntaxes. People only think they are much different because the lack exposure to languages from other (or no) heritages.
It doesn't matter how diverse the syntax is, just think of the vastly different worlds of people programming in C derived syntaxes:
The enterprise app developer writes Java for her day job, and spends her nights creating iPhone apps in Objective-C. Her apps connect with an API on the website she built using Ruby on Rails, and handles front-end interaction in JavaScript.
All four languages are syntactically similar, but each has vastly different application domains.
Do you anything about Forth and Prolog and the languages you mention? Three are the same paradigm, the other two are very much not. This has nothing to do with syntax or "application domains".
