A source of reference is nompuq, but I'm not sure that's the right word to use here. There's also the word mung meaning "origin", so you might say for instance:
mu'tlheghvam mung vISov/vIyaj. ("I know/understand the origin of this sentence.")
You might also use the word ghov ("recognize"):
qIDvam vIghov. ("I recognize this joke.")
I get that a lot too - and I take great pride in it as well. :)
When I was living in Germany when I was younger, most people were surprised to learn that I was a foreigner, as I spoke German well, with only a very slight accent. Usually, they guessed I was either Polish or French. When I finally did tell them I was American, the usual reaction was shock and surprise, followed by some variation on "But you CAN'T possibly be American. You speak German so well!" Kind of the same idea as the original joke.
For the record, as a non-American, I don't approve of people dissing Americans as a group ... although it can be quite fun to tease the ones you're on good terms with ;)
I had a similar experience in Japan, last week, as knowing pretty much any amount of Japanese is considered pretty much god-tier over there :P
At least half of humans speak more than one language, and some estimates are up to 75 percent of us, I guess depending on how well we speak it in order to be counted. https://www.bbc.com/future/article/20160811-the-amazing-benefits-of-being-bilingual
I do have only heard the punchline as "American." I'm told that if your first language is English, you can graduate from high school there without having ever studied a second language, but that might be old information.
Does SW stand for Star Wars? Han Solo seemed human and he had at least a listening knowledge of the languages spoken by Chewbacca and Jabba.