There's a lot to be said for this kind of approach. My job takes me all over town and sometimes I go into black neighborhoods in South Atlanta where I am the only white guy and I stick it out like a sore thumb. It was a little tense at first but I quickly learned to just brush it off and act normal. I've never had a problem and now after doing that for years I've got some pretty good friends down there. Just the other day we were laughing and joking about privilege meaning that they don't have to buy sunscreen like I do.
In the scenario you describe, I don't try to speak the "language". If I don't understand something, I'll tell them.
I think it would sound dumb for a guy my age to try and use the same slang they're using, white or black.