Can speaking slang in another language help you understand subtle differences in meaning between languages?

In every culture, we have our own slang, idioms, sayings and culturally specific humor that loses much of its meaning and/or effectiveness through translation. I think that by trying to figure out the origin of common vernacular gives us greater insight into the actual usage of another language, and how it is manipulated by its native speakers.

 

Do you think that it would be helpful, and potentially more interesting, engaging and modern for students to be able to speak the common dialect of a language, as well as understanding the grammatical aspects of it? 

How do you say "What is your goal in life?" in Spanish?