The mIRC scripting language can only be as buggy as a coder makes it. mIRC itself may have the occasional bug but no more than any other programme out there. If mIRC has trouble reading it's own scripting language then it's likely to have trouble reading any language.
Languages like Perl are totally un-necessary, especially for established clients like mIRC that have evolved over years doing what it does best, providing the IRC community with an "allrounder" client to use on IRC with an easy to read help file, reasonably easy scripting language (noting that even this isn't for all people) and a tonne of voluntary support around the world.
mIRC is popular because of what it is, not because of what some people want it to be.