How does a program composed of several languages work? How do the languages work together or interact with each other? How do they understand stand each other? How do you know when to use any given language and how do you implement them so they work together? (Not in terms of strengths and weaknesses but in terms of task and function). This isn't a WHY would you use multiple languages question but a HOW would you use multiple languages question.
Feel free to direct me towards any resources that may prove helpful in my quest for understanding.