Language can cause confusion even when two people aren't using separate languages. Often, it's enough for them to speak different dialects of the same language. This trope applies when the differences in dialects of a common language are used for humor or characterization. Most of the examples here are about the differences between British English and American English, but this can occur in any pair of dialects, in any language.
Confusion over dialects in Real Life varies from person to person, and depends on the situation. If British Alice says "throw it in the boot" to American Bob in a story, without context he may be confused; but when they're obviously near to a car, it isn't a huge leap that she means that something should be put in the "trunk".
It can also be a giveaway when a writer sets a story in a land besides his native one. Many English and Canadian writers write for American audiences. Often they're so good at it that the reader doesn't notice—until a Texan character mentions something that happened "when I was at university." (An American would say "when I was in college" or "...in grad school", even if he got his degree at a university)note This is because the line separating a "University" from a "College" is nearly nonexistent in the USA... and "college" frankly takes half the effort to say and spell.
People who read or watch a lot of fiction in another dialect will understand more words than expected, which may even be Lampshaded by the writers. Before the rise of the Internet in the early 1990s it was posited that the different versions of English might eventually diverge into separate languages, however these days the Internet has made it possible to inexpensively speak to a friend in a like-language country on a daily basis in both text and voice - plus watch their TV shows and play video games with them, so time will only tell.
See also Australian English and Did Not Do the Bloody Research. Contrast Language Barrier, which is Separated By Lack of a Common Language.
Do not add Real Life examples here. For Real Life examples, see the Useful Notes page.
Examples in fiction and media:
Anime and Manga
In Detective Conan, the different meanings of horu (see Useful Notes page) were used to identify the criminal who came from Osaka.
"Knocked up" gets used in Supergirl, when the British-accented demon Buzz asks Linda to knock him up in the morning. Eventually they get it sorted out.
One Buffy the Vampire Slayer Season 8 has Faith go undercover to defeat a rogue slayer. The other slayer asks Faith "Do you mind if I bum a fag?" It takes Faith a moment to realize it wasn't some kind of Double Entendre.
In an eighties Justice League comic, The Flash (who has no Secret Identity here) introduces himself as "Wally" to a group of English girls, who respond with derisive laughter. Afterwards someone explains to him that "Wally" means idiot. It's a very gentle insult, like something your nan would say. Using it non-jokingly would be seen in a similar way to Have a Gay Old Time.
Barbara Stanwyck plays a con woman in Screwball ComedyThe Lady Eve. When she is pretending to be the Lady Eve Sidwich, she leans on this trope pretty hard, dropping a lot of British slang to the befuddlement/amusement of her American hosts.
In Paul, two British comic-book nerds attend Comic Con in San Diego and then go on a road trip in the American Southwest. Clive asks where they parked the RV.
In America, "pissed" means angry; in most of the rest of the English-speaking world, it can also mean "drunk", while angry people tend to be described as "pissed off" rather than just "pissed". On the commentary for Shaun of the Dead, it's stated that the only thing they consciously did to avoid confusing Americans was to say Mary the zombie was "so drunk" instead of "so pissed", because they were aware of this trope and knew how that would sound.
The meanings of "pissed" led to a memorable scene in the Bob Dylan documentary Dont Look Back. In a hotel in London, Dylan (who is American) threw a fit when someone threw a glass out the window. The guy was drunk and tried explaining that he was pissed, so Dylan said something along the lines of "Oh, you're pissed?! Don't tell me you're pissed!"
In Austin Powers in Goldmember there's a scene where Nigel Powers is talking about his sexual exploits and Austin requests that they speak in "English" English (actually Cockney rhyming slang) in front of the Americans. The proceeding conversation has subtitles, though not all of it, as Even the Subtitler Is Stumped...
In "Money, A Suicide Note" by Martin Amis, the main character is sent to try to get a very clean cut actor called Spunk Davies to use a stage name instead.
In Good Omens, Newton Pulsifer has a Witchfinder's card which states that faggots (meaning chunks of firewood) should be turned over to him. When an American soldier asks what they do with the faggots, Newton replies "We burn them." The soldier is quite impressed...
Though most of these are now obsolete, G.K. Chesterton notices a number of these Anglo-American differences in his writings. He was told that a lady journalist had referred to him as "a regular guy" and did not see how that was meant to be complimentary; in the American usage of the time, the phrase meant "someone who was affable and not snobbish", whereas in the British use then current, it meant "a figure designed to be mocked, a scarecrow, or an object of ridicule". He was warned by an American friend against certain people because they were "very bad actors"; GKC did not know why their defective thespian abilities should cause him anxiety, until it was explained that this was American for "malefactors". Similarly, an American friend told him her sister had "gotten a beau" — by which he understood her to have devoted herself to archery.
Not too much between Charlotte and her cousin Zee in the Cronus Chronicles, but there is a little bit of idiom confusion when they first meet, especially since Zee is an avid (British) football player.
Live Action Television
Weaponised in Sherlock. After finding a connection to America in "The Hounds of Baskerville" case, Sherlock deduces the murderer’s identity, and cites, among other evidence, their former suspect’s use of the word cell phone – as opposed to mobile – due to time spent in America.
In episode "Internal Audit" from Elementary, Sherlock meets someone new.
Randy: You're Sherlock, right?
Sherlock: And you are?
Sherlock: Name or adjective?
Sherlock: Short for "Randall" or state of sexual arousal?
Randy: Are you asking me if I'm horny?
Since Daphne, a Brit, is a major character in Frasier, this trope comes up fairly often. For example:
Frasier: Is Dad home?
Daphne: Nope, I haven't seen him since he knocked me up early this morning.
Daphne: Knocked me up. Woke me up. It's an English expression. What does it mean here?
Frasier: Oh, something else. You'd definitely be awake for it, though.
Spike: (checking the label in his jacket pocket) "Made with care for Randy"? Randy Giles? Why not just call me "Horny" Giles, or "Desperate-for-a-Shag" Giles? I knew there was a reason I hated you!
Giles: Randy's... a family name, undoubtedly.
An episode of Have I Got News for You had lots of fun with the fact that there's a staffer in the Obama White House named Randy Bumgardener. To elaborate: Randy = horny. Bum = ass. Gardner = "Uphill gardener" (a rarely-used slang phrase referring to a gay man).
An episode of The Graham Norton Show in the UK had this confuse guest Johnny Knoxvile after an audience member tells Graham on how she stuffed a rubber up her nose. Johnny's reaction led fellow guest Catherine Tate to tell him it's an eraser. Graham was very amused.
Nicely played with in Blackadder Goes Forth, when Melchett assumes the crossdressing George is a woman and says she's "full of spunk." Blackadder is quietly amused.
This gag from The Office (UK) was made funnier by Keith's general creepiness and monotone delivery.
Keith: "Fanny" means your arse. (Beat) Not your minge.
Duncan refers to leaving his wallet "in the back of my lorry", presumably because someone heard that 'lorry' is British English for 'truck'. In fact it suggests that the psych professor mysteriously owns an 18-wheeler - pickup trucks are hardly ever seen in the UK, and when they are they're called 'pickup trucks'. Not to mention that, as shown in the pilot, Duncan doesn't have a pickup truck at all; he drives a Smart car.
Duncan also states that he grew up on "52nd Street in Islington". Assuming he means Islington in London, not only is there no such street, but in British cities streets are usually named, not numbered in the same way that they often are in American cities.
In-universe example: "Let's blow this pop stand and head out back for a spot of slap and tickle. That's sex, in case the lingo hasn't made it across the pond."
...all of which are part of the larger joke that Duncan doesn't actually know any English slang and knows very little about England, having come to the US at a young age with his grandfather.
The word 'rubber' means an eraser in the UK, but in other places (particularly the USA) it's a condom. As a guest of his Late Night show, Emma Watson told David Letterman that she committed this infraction during her first semester at an American university (Brown), asking a male classmate for a rubber during class.
In iCarly, Spencer orders Canadian bacon, only to find out that it's just sliced ham.
Gwen:I had to go to the petrol station and all they had was crisps. Esther: I think you mean "gas station" and "chips." Crisps are called "chips" over here. Gwen: Thank you, Miss Translation. Esther: And a mobile is a cellphone and by cashpoint I think you mean ATM. Gwen: Don't ever leave my side. shortly afterwards Gwen: This lemonade is flat. Esther: It's lemonade. It's supposed to be flat. Gwen: What, fizzy fizzy lemonade? Esther: It's fizzy in the UK and flat in the US. Gwen: Yeah, that just about sums it up.
'Shit' can mean 'stuff' in American or Australian English, though it's still connected with the original meaning. In British English it remains a profanity in any context. Stephen Fry once pointed out that if an American says: "I was eating hamburgers and shit", you can tell what he means. But written down it looks like he's saying: "I was eating hamburgers and shit."
In one episode of Law & Order: Criminal Intent, Detective Goren deduced that a kidnapper was British and not American because he threatened that if he wasn't paid his ransom, "it wouldn't be a very happy Christmas." An American would have said Merry Christmas.
"The Gambler Song" (a parody of the Kenny Rogers song "The Gambler") by Australian comedian/singer/songwriter Martin Pearson contains this lyric:
"Then he bummed a cigarette/
(Most people smoke them with their mouths)"
The differing meanings behind the word "thong" were used as a joke in the comic strip Zits. When Connie expressed a desire to wear thongs, it was quite the mental image for her son Jeremy. It is actually a language difference within America; certain parts of the country (and older folks) use the more English-y term "thongs", whereas everyone else uses the less-ambiguous "flip-flops".
The Bob & Tom Show: In "Cooking with the King", Elvis goes to England to try fish and chips and is completely confused by his host Ian St. Ian's speech. Eventually they get into a fight over the chips, which Elvis recognizes as French fries ("And they ain't even Ore-Ida's!").
Stand-up and Recorded Comedy
Jasper Carrott once built an entire routine around the idea of going into an American shop to buy a pencil eraser.
Jasper: Hello, can I have a rubber please?
Storekeeper: How many would you like, sir?
Jasper: Just the one! Gawd, I don't make that many mistakes!