Which engine / coding language is currently the most promising in terms of sales?

[Till]

Oh yeah it'll take time alright. Going to school for this stuff is probably the best bet.

C++ is probably a big one, also one of the hardest to learn apparently. Unreal Engine is written in C++. Then there's C# which the Unity engine is written in.

Then there's Python which is supposed to be easier.

As for selling stuff I have no idea.

To sell your wares you'll need a website therefore webmastering and server-side coding will be necessary unless you want to pay someone else to run your site. I agree with you on all points, C++ and Unreal Engine will suffice for software and game development, I'd like to mention learning PHP as well for webmastering.