Hi to all indonesian simutrans players.
Making whole new pak involves huge amount of work. You'll have to make everything new. Not only vehicles, but also roads, tracks, buildings, industries, attractions, signals, trees, etc, etc... I would recommend you, to focus on making just a nice set of addons of indonesian vehicles. And if you would feel that vehicles are not enough, can continue with buildings or attractions. You can set climate to tropical, so that they appear, where appropriate. And if they are nice, perhaps Leartin will include them in the main comic pak.
But keep it as addon for pak192.comic. Thus you could focus on little things and have a playable game.
Believe me, I am one of the maintainers of pak128.CS (czechoslovakia), and we still miss lot of important objects, to have the pak complete. (And industry is just copy of pak128).