I don't believe variadic functions are supported. I've seen a discussion or two about adding them to G4 in the github, but I don't think any of them actually made it in.
As a work around, this could be done with something like a Array. Just a shot using your example:
print("xxx: %s" % [args])
my_print([2, 3]) // "xxx: [2, 3]"
var a = "a"
var b = 2
my_print([a, b, "cde"]) // "xxx: ["a", 2, "cde"]"
Could have conditions in the method that check the size of the args array. Additionally this could also be done with a dictionary instead of an array.