In most cases Core C / C++. But I have seen cracks build on .NET too but very few. Peoples figure out the algorithm used to generate Key's and develop a program same as the product manufacturer which generate keys for sell.
Intro Demos are simple videos which is integrated in the application itself.
Trial versions are programs with limited capabilities which gets decided by the Keys used.
Trainers are part of the program. Or you can say a copy of the same product which is limited to click on highlighted areas as per the tutorial goes on by restricting clicks.
And regarding size, don't think integrating videos and all will raise the size in that way you are thinking, as exe is highly compressed.
One I came across a crack which was about 10MB or something but it extracted the thing to around 700MB. It use Uharc