This trope goes back quite a ways in American television, almost to the point of being a Dead Horse Trope, without passing through the stages of Clever Idea -> Trope -> Subverted Trope -> Discredited Trope. (Mainly because its roots are another fifty years back, in vaudeville.) The characters — some portrayed as being Jewish, some not — will pepper their dialogue with words and phrases in Yiddish (or more specifically, in Yinglish). Translations and subtitles are not provided, and meanings must be inferred from context. This occurs in both dramas and sitcoms, sometimes without regard to the setting city of the show, though it most often appears in shows set in New York, where it's most common in actual speech, and Los Angeles, where schmooze — a Yiddish word if ever there was one — is a way of life. The criminal argot of East End London Gangsters has also absorbed a few Yiddish words.
Thanks to this trope, however, several Yiddish terms have become a standard part of American English vernacular. Concentrated in large American cities and spreading out worldwide, common Yiddish terms like "putz," "schmooze," "Word Schmord," are slowly becoming standard English words. Even idioms that sound perfectly American, like "Eat your heart out" or "What's not to like?" are calques from Yiddish, still preserving the original Yiddish speech patterns. This trope evolved from the early movies and TV — censors were aggressive in editing out curses, sexual references, etc. However, most of these early censors did not speak Yiddish, so the writers, actors, and producers (who often did) used Yiddish curse words as a way of Getting Crap Past the Radar.
If a character speaks in Yiddish as sole proof of Jewish authenticity, then they may be practitioners of Informed Judaism. If a senior character has the accent as well, they're an Alter Kocker.
A rather interesting survey on the Real Life spread of Yiddish words and phrases, Hebrew words and phrases, and New York regional features, both within and outside of the Jewish community, can be found here.
Compare All Jews Are Ashkenazi, Jews Love to Argue.
See As Long as It Sounds Foreign, Pardon My Klingon, You Are The Translated Foreign Word.
Spider-Man, particularly the Ultimate universe version, is fond of peppering his speech with random Yiddish, especially during fights — despite the fact that he's Lutheran, not Jewish. But then, he's from New York City. In fact, his home neighborhood in Queens, Forest Hills, is very Jewish.
Mary Jane: Where do you know Yiddish all of a sudden?
The Thing from the Fantastic Fouris Jewish and often peppers his speech and battle banter with Yiddish words and phrases.
Shaloman. All together now... "Oy vey!"
Marville has hadrosaurs using the Hebrew word "mishbucha", during the Jurassic period. If this strikes you as in any way coherent or logical, seek help.
One of the best examples is this scene from the opening of the 1932 Warner Bros. picture Taxi, in which a Yiddish-speaking Jewish immigrant is frustrated in his attempt to communicate with a policeman, until Cagney interrupts in fluent Yiddish to offer the man a lift. Supposedly, the scene was actually improvised, to take advantage of the fact that Irish-American actor James Cagney had learnt Yiddish from his playmates while growing up in New York City. The presence of the perplexed Irish cop only makes it ten times funnier.
A wonderful instance appears in the film A Mighty Wind: Ed Begley Jr. plays Lars Olfen, a first-generation Swedish-American Public Television executive who nonetheless laces everything he says with a vast amount of Yiddish:
Lars Olfen: The nachesnote joy that I'm feeling right now... 'cause your dad was like mishpochenote family to me. When I heard I got these ticket to the Folksmen, I let out a geshreeyehnote squee, and I'm running with my friend... running around like a vilde chayenote wild beast, right into the theater, in the front row! So we've got the shpilkesnote nervousness, 'cause we're sittin' right there... and it's a mitzvahnote good deed, what your dad did, and I want to try to give that back to you. Okeinhorehnote not the word he meant to use; alav hasholem means "rest in peace," this is more along the lines of "knock wood", I say, and God bless him.
A common gag in Mel Brooks films, usually doing them himself.
The Yiddish-speaking Indian chief in Blazing Saddles. His headdress actually reads "Posher l'Kesach": roughly, "Posher for Kassover." When he meets Bart's family, he says in Yiddish, "Blacks!" When one of the other Indians raises his tomahawk, Brooks says, "No, no, don't be crazy. Let them go!" After Bart's family has ridden away, Brooks mutters, "Have you ever seen in your life?" He finishes in very Yiddish-accented English, "Dey darkuh den us! Wuff!"
Mel Brooks as Yogurt in Spaceballs drops some Yiddish, such as, "The ring was bupkus!" Also, when about to translate the words on the medallion, he makes a bunch of croaking noises that are probably supposed to lampoon the fairly guttural sound of Yiddish. He's just clearing his throat.
Eddie Murphy's urban conman running for Congress in The Distinguished Gentleman impresses a Jewish senior citizen by contradicting her in Yiddish, which he apparently picked up playing gin on Miami Beach. He is also shown driving through several neighborhoods while talking on a megaphone using an accent common to each neighborhood, including sounding like an old Jewish man with Yiddish-peppered sentences.
Lock, Stock & Two Smoking Barrels pokes fun at London gangsters not realizing the origins of their slang when Tom assures Nick the Greek that a deal is "kosher as Christmas," to which Nick answers, "Jews don't celebrate Christmas!"
An extended joke in the erotic thriller spoof Fatal Instinct: the hero's wife and the man she is having an affair meet in a park to discuss murdering the hero. She suggests they speak in Yiddish and they both converse fluently for several minutes in the language before the elderly black man on the opposite bench interrupts with a helpful suggestion. He can't speak Yiddish but he can "read subtitles".
In Robin and the Seven Hoods, Frank Sinatra at one point feels like he's being noodged. "It's an old Italian word."
In City Hall, Mayor's aide John Cusack (who's supposed to come from Louisiana) mispronounces "schtick" as "stick", prompting Bridget Fonda to snap at him to "get the cornpone out of your Yiddish" if he's going to get anywhere in New York City politics.
In Mary and Max Max says a phrase in Yiddish whilst mailing a letter to his penpal Mary.
Perhaps to lend Gotham City that Big Applesauce frisson, Max Shreck (Christopher Walken) in Batman Returns was originally supposed to sprinkle a few Yiddishisms into his dialogue when speaking with the Penguin, Selina Kyle, and other characters. (Interestingly, Walken is from New York and actually does know some Yiddish.) A good example is (while consoling the Penguin about his failure to kill Batman) "So he survived. C'mon, be a mensch - stand it" (whereas in the finished film, the line is just "So he survived. What's the worry?"). He also was supposed to use the word goniffs ("thieves") in one scene in his office; and after tricking a circus monkey into giving him the keys to the cage in which the Penguin has him imprisoned in his hideout, he was supposed to say, "Thank you, you schmuck!" The screenwriters excised these lines probably because they feared that American audiences not living on the East Coast - not to mention foreign audiences - wouldn't have a clue what Max was saying.
This abounds in the works of Harry Turtledove, most prominently in those sections of his World War series featuring the Russie family, and also in several sections of his American Empire trilogy. While what they say always fits with the meaning of the word, they are sometimes idiomatically incorrect — no one would actually use the word the way the character does.
Michael Chabon's The Yiddish Policemens Union, an Alternate History mystery featuring a Jewish refugee state in Alaska. Almost all the Jews who immigrated there are Ashkenazi and they interact with few outsiders, so Yiddish has been adopted as the standard language. There are even a few Yiddish/English puns, such as calling a handgun (a "piece") a "sholem," meaning "peace."
Miles Vorkosigan uses a noticeable amount of Yiddish words, despite living around 1000 years in the future. He is portrayed as having an above average knowledge of the past, but it's interesting that this part of a High German language of Jewish origin was preserved.
Given that Barrayar had a huge Russian influence, and modern Russian can be compared with New-York English in its level of Yiddishisms, it's not that surprising.
The classic science fiction short story "A Martian Odyssey" by Stanley G. Weinbaum includes a German engineer named Putz.
Esther Friesner's novel Elf Defense includes among its minor characters a classic Tolkien/Shakespeare-style elf maiden whose speech is unexpectedly punctuated with the occasional bit of Yiddish. When called on it, she abashedly admits to dating a dybbuk (a possessing demon of Jewish myth).
In respect to the influence of Yiddish on British criminal argot, this probably explains why a Redwall character who was a Lovable Rogue ended up with the name Gonff (goniff is Yiddish for thief). In a more general example, the phrase "keeping shtum" (quiet in the sense of "not snitching") is much more likely to be heard from a London Gangster character than a Jewish one.
In Feet of Clay all of the golems' names are Yiddish; these names include Dorfl, Schmatta, and Klutz. The golem who goes mad is named Meshugah.
In John Moore's Fractured Fairy Tale, The Unhandsome Prince, Rumplestiltskin never actually admits to being Jewish (in a world where antisemitism is definitely a real thing), but he seems to drop a lot of Yiddish into his conversation, and he becomes much more interested in Rapunzel when he finds some clues that she may be Jewish.
In Primo Levi's Holocaust memoir If This Is a Man, many of the Jews in Auschwitz overcome the Language Barrier by using Yiddish. A certain tension rises between Yiddish speakers (mainly Poles and other Eastern Europeans) and non-Yiddish speakers (mainly Western Europeans, such as the Italian author).
Rivka's (The Second Mango)unnamed native language contains several Yiddish words and phrases that she peppers her speech with
Alien Nation: Francisco and Sykes consult a doctor of Tenctonese medicine, who peppers his speech with Yiddish words.
Howard's mother in The Big Bang Theory often uses terms such as "ferkarkt" and "putz" in regular speech. She even taught Howard's (non-Jewish) fiancee Bernadette how to use the latter.
In ER, Dr. Greene is treating an elderly Jewish woman who says she needs a CT scan like she needs a "loch im kopf." (that's "a hole in the head" for the goyshe tropers) He responds that the CT is to make sure she doesn't have a "loch im kopf" and reveals that he is ancestrally Jewish, leading the woman to agree to the test.
Grace: I can't hear anything over that fakakta harp.
The "Weird Al" Yankovic song Pretty Fly for a Rabbi features Yiddish liberally sprinkled throughout the lyrics. When asked how he knew the Yiddish, Al replied: "A good percentage of my friends are Jewish, and most of those Yiddish words are fairly common usage — in the entertainment industry, anyway. Also, I bought several English-Yiddish dictionaries for reference."
The Joker, in Batman: The Animated Series, often threw in a Yiddish word when searching for another adjective to drive his point home, although probably out of many Yiddish terms being Inherently Funny Words. Harley Quinn being Jewish, used plenty too.
The Disney version of Hercules managed to have Hades (and Phil) throw various Yiddishisms into his speech, despite ostensibly being from ancient Greece.
In Brandy & Mr. Whiskers, Mr. Whiskers' brain speaks with a Yiddish accent. Whiskers himself does not. Whiskers appears to be capable of thinking on a Whiskers level without the aid of a brain (the plot of at least two episodes revolves around Whiskers' brain getting fed up with being ignored, and leaving), so maybe it's not so surprising.
Larry of Time Squad often says "Oy vey!" when dismayed. Seeing as he was originally designed to be a polyglotic diplomat, this is rather appropriate.
The Critic's Alice Tompkins: "Honey, we have a saying back in Tennessee: 'Be a mensch, not a schmendrick.'"
The Simpsons: Krusty the Clown is fond of spouting Yiddish words, like ferkakta.
One episode of The Mighty Ducks featured a wise old duck who taught Grin how to keep his head while playing hockey. At first, he looks and talks like a stereotypical Fu Manchu Chinese-type, but suddenly shifts into stereotypical Yiddish blabbering without any warning. Keep in mind, he's from another planet, in a different dimension.
In Hey Arnold!, Harold is Jewish and once used the word "Kibitzer" Yiddish for a non-participant person, offering (often unwanted) advice or commentary. To describe Arnold's tendencies to butt in to other people's business. "Yutz" has also been used by a few characters in the series, mostly by Helga.
Onhengerarbetn (Fan Works)
DC Nation's Sue Dibny peppers her dialogue with a few choice Yiddish phrases, but only if she is really ticked. Dr. Light wound up with a real earful before she and Constantine all but tossed his sorry hide out an airlock.
Played with in The Producers (the musical), in "The King of Broadway."
Max Bialystock: I'll never forget, he turned to me on his deathbed and said, "Maxella, alle menschen muss zu machen, jeden tug a gentzen pisch pippikachen!"
Crowd: What does that mean?
Bialystock: Who knows? I don't speak Yiddish. Strangely enough, neither did he.
Even the NAZI speaks Yiddish in the musical.
"So ve hop our hops, Und ve clop our clops, Und ve drink our Schnapps 'Til ve plotz!"
In Fiorello!, La Guardia says he's half-Jewish when campaigning among the Jews, and sings a Yiddish version of his campaign song ("Ich zug tsu eye-ich, Tammany is nisht kosher").
In the musical Little Shop of Horrors, the plant knows some Yiddish, like "Come on Seymour, don't be a putz". (I mean, come on, he even says "Feh!") He probably learned the Yiddish from the likely-Jewish Mr. Mushnik, who uses "mensch" and "mishegas". The lyricist/composer team, Ashman and Menken, also did many Disney movies, and the same influence is seen there (Phil in Hercules, etc.).
It's in the original film as well.
The musical In the Heights, which takes place in Washington Heights (upper Manhattan with a predominantly Hispanic community), has several Latino/Latina characters use Yiddish rather believably in their daily conversations, similar to their usage of Spanglish (although less frequently, for obvious reasons). Prior to a wave of Puerto Rican and Dominican immigrants into the area Washington Heights was a rather Jewish neighborhood, and the characters probably picked it up from one of the innumerable senior citizens with a rent-controlled apartment dating back to the 40s — in which case the Lenny Bruce quote above becomes applicable.
During "It Won't Be Long Now" Vanessa tells Usnavi he has "some schmutz on his face" from fixing the refrigerator.
During "The Club," Usnavi and Benny are trying to drink away their troubles and Usnavi says "As long as you buy 'em — L'chaim!"