Hi Susanna!
What a great idea for a thread!
Part of God's calling in my life seems to have me talking to people of all ages, so I find myself having to keep up on a lot of pop culture. I listen to a lot of social commentary channels from all ages, from teens to retirees, and that helps me learn some of the lingo. It really is a form of learning other languages, just like you said.
It's kind of a sad fact of our society today that most people seem to expect others to cater to them -- they will complain about other people not being able to make good conversation, but the truth is, it's because they want others to bend around the things that only they are interested in.
I've found that for me, the best way to reach people is to try to learn a little of their "language" and show genuine interest. There are basic questions you can ask about their interests -- What got you interested in X? What do you enjoy most about it or find most challenging? Etc., that can really apply to pretty much any hobby or activity in existence. And people love talking about what interests them (most, however, seem to fail to ask the other person what THEY'RE into and then show genuine interest as a common courtesy, but that's another issue.)
Many people have probably heard of the Rosetta Stone -- it was instrumental in interpreting Egyptian hieroglyphics because one of the languages written on it was Greek, which was a known language, so they could then compare this known language to the unknown language of hieroglyphs.
Many times when I'm talking with people, or even writing threads here, I ask God to "please give me a Rosetta Stone" -- something general that an audience can relate to, and I can use as a stepping stone for conversation.
I might not know about cars, but basic questions ("How did you get into cars?" "What was your biggest DIY repair job?") can be molded to most any subject.
And if people use lingo I don't know... I look it up -- or I just go ahead and ask, as the risk of sounding stupid and uncool.
But that's the beauty of getting older.
We don't have to care so much about whether we sound dumb or square -- we know what we know, and, when reaching out to others, we don't care so much about putting our image on the line.

(We can always just blame it on being old and senile.)