I think this code looks quite well written and concise.
I am however curious as to why the use of %dir, when its only purpose as far as I can see is to be put in another var. Aside from managability of the code of course.
Since the content of %dir seems to be quite static as well and its only use is to be put to use inside the $findfile, why not just put the written out dir there?
So instead of:
var %dir $+(scripts\,JSON-For-Mirc-1.0.4000)
var %file $qt($findfile(%dir,JSON For mIRC.mrc,1))
You can make it:
var %file $qt($findfile(scripts\JSON-For-Mirc-1.0.4000,JSON For mIRC.mrc,1))
Another smaller related point: for the static info you have in %dir, there's no need to put the content within a $+().
//var %test $+(scripts\,JSON-For-Mirc-1.0.4000) | echo -a Result: %test
//var %test scripts\JSON-For-Mirc-1.0.4000 | echo -a Result: %test
And now, I'm going to go read up on $urlget