Often the language isn't the big part of the pain on a project. Often it's the speciality libraries that will consume your time. For example, in Windows, you will get some kind of library with window features and functions. Whatever library you use will be where you spend a lot of your time. And that will be specialized to that library on that platform, because it will have quirks and weirdness. And may be documented less well than ideal. And when you join somebody else's project, you may not get a choice on what libraries you are using.
As cpscdave suggests, once you learn a language or two, the next language is a lot easier. The only thing is, will you learn a given style of programming? For example, will you learn object oriented? Will you learn structured? Will you learn some other approach? And will you learn development cycles like rapid prototyping, classic waterfall, and so on? That will depend a lot on what the projects are that you may join.
There are a ton of books out there on any of these subjects. It will be tough to figure out which one to read first. One very good general book on doing a good job at the coding task is _Code Complete_ (now in the 2nd edition) by Steve McConnell. Excellent book, highly recommend. Once you get some of the basics of coding well, then go find books on the specific task or approach.
There are lots of other subjects: documentation, testing, interface design, source code control, all up and down your arm with a long shopping list. You can't learn them all at once, so you need to pick what you have time for now.