Adding another language wouldn't be that hard. Actually, we had
another one before nasal and beside nasal for a while. It was
called PSL (plib scripting language), and we ripped it out because
Nasal was/is just better and because offering and maintaining two
languages it utterly pointless .
And that's why I consider the likeliness of getting lua or any
other language support committed approximately zero. I for one
would strongly oppose ("veto"-style :-). Of course, what you do
in your private copy or fork is your business.
Let me jump in with some pre-coffee comments (so I'm not yet responsible for anything I say) :-)
Nasal is *very* well designed, compact, and efficient. It is used heavily throughout many areas of FlightGear. So I can't imagine any scenario where we would switch to some new scripting language unless a lot key developers were convinced that it was every so much better that that benefit would substantially outweigh the cost. And I find that scenario hard to imagine.
I agree that if you want to play around with integrating Lua into your own development tree, that's great. You will learn a ton about flightgear and it's internal structures in the process.
I tend to side with others that there would need to be some overwhelmingly compelling reason to support lua along side Nasal within FlightGear. If the primary motivation is language preference, that is going to be a really tough sell around here ... and that is because Nasal is *really* slick, brilliantly conceived, well implemented, and it has served us so well.