What are different ways that web applications are built to handle multiple languages?

Question

I am hoping to get an understanding of all of the ways that multi-language websites/apps are built. What are pros and cons to each? Do you have to have a separate url for each language? If you are not using separate urls, how do you dynamically change display language? Can you use cookies to change display language based on a drop down?

This is a pretty open ended question because I'm not very knowledgable about this and not exactly sure what targeted questions to ask. Would greatly appreciate shared experiences and best practices for how multilanguage websites are architected.

Thanks!