Learning the unfiltered side of a language is definitely a secret weapon for sounding like a native, but it is best used as a supplement rather than a replacement for grammar basics. While classroom learning gives you the structure you need to build sentences, slang and swear words provide the emotional texture and rhythm that make you sound like a real person rather than a textbook. I found this to be true when I lived abroad; picking up local idioms allowed me to participate in jokes and show I understood the cultural vibe, which made people much more comfortable opening up to me. Just be careful, because using slang without knowing the proper context can sometimes backfire or make you sound aggressive if you are not careful. Ultimately, the fastest path to mastery is combining the structural foundation of formal study with the social connection that comes from learning how locals actually speak in the real world.