Lisp is not going to be much use for you if you're interested in game development. It would be more useful to ask what possible reason this "organization" has for such a strange policy, and what possible languages they could be prescribing.
Note there are very good reasons that the majority of programming languages disallow
- in identifiers (and also any other operators like
& etc). Consider the following:
var a = 5
var b = 2
var a-b = 1
var c = a-b # what is c? 1 or 3?
Allowing this would make it impossible for the compiler to know whether you meant a variable name or an operation there.