Being of a certain ethnicity doesn't necessarily mean someone speaks a certain language or even knows much of their heritage. Just because someone is of Mexican descent and their parents speak Spanish doesn't mean they will also be fluent in Spanish. Nor do they necessarily know much about their food or other aspects of the culture.
There is Truth in Television in this. For example, studies show that each generation living in a certain country are less likely to be bilingual than the preceding one. So a person who moved from South Korea to Canada will often have grandchildren who can't speak a lick of Korean. People who do not speak the language associated with their heritage can be made to feel embarrassed or awkward for it, or might have internalized feelings of inadequacy due to their lack of understanding, which may opt them to learn it as a second language later in life.
- A Spanish language Goya commercial has a young latina girl telling her mother that she has to make a cultural food for school. Her choice? Nachos. Her family is horrified and they end up making flan instead.
- One episode of Chihayafuru has the characters going against a group of "foreigners". They begin speaking in Gratuitous English with Japanese accents and mispronounce their words. This however was intentional. The characters were raised in Japan and can barely speak English. They were pretending to be from another country to freak out the competition.
- Fifth grader Ana Coppola of Strawberry Marshmallow has lived in Japan for as long as she can remember. She and her family have integrated to such a degree that Ana has next to no English skill whatsoever and is generally more knowledgeable about Japanese culture than her Japanese peers. This bothers her enough that she tries to ramp up how foreign she is at school and works with her classmate Matsuri to re-learn her mother tongue.
- Massugu ni Ikou: Hanako didn't know she was a Kishu until she overheard her vet mention it.
- This is the initial conflict of Double Happiness. Tom, a Chinese-American from Brooklyn, moves in with some relatives in San Francisco's Chinatown. He doesn't recognize the culture, the food, or even the language his relatives are speaking. This leads him to fear that he's too white to be Chinese.
- Diary of a Tokyo Teen is an autobiographical comic book about a teenager's visit to Japan. She was born in Japan but moved to America at a young age. She's visited Japan before but there's still a culture clash.
- Dick Grayson was retconned as Romani in the late 1990s. It's been shown that he doesn't know much about his heritage and doesn't understand the language.
- In Heis'he Ri'nanovai, Morgaiah t'Thavrau has to explain an aspect of Romulan homeworld noble culture to her executive officer Sarsachen tr'Sauringar, who though also Romulan, grew up as a commoner on a border colony and spent fifteen years in Starfleet.
- Downplayed in the Jem fic Starlight Is For Always. Because of her Latin surname, it's thought that Pilar can understand Spanish, but despite her Mexican-American parentage, Pilar only understands English.
- In Sweet Country, it's a recurring theme that the Aboriginal characters working for the white settlers are cut off from their ancestors' culture, many of them having been separated from their culture as children. When Sam and his wife flee into Aboriginal tribal lands, they're almost as out of place there as the white posse pursuing them.
- Half-Jewish on his father's side and half-Puerto Rican on his mother's side, J from I Am J was raised rather nonreligiously. His father rarely brought up his Jewish heritage or faith and only briefly tried to "act Jewish" when J was ten. As a result, J is pretty clueless on Jewish culture. He does remember one prayer, however.
- Daya from Orange Is the New Black gets scorn from other latina inmates (even her own mother) for being Puerto Rican but being unable to speak Spanish.
- Ana Sofia from Telenovela is the lead of a popular Spanish telenovela but can't speak Spanish at all. Hilarity Ensues.
- Duncan from Community often uses incorrect British terminology as part of a joke. He has lived in America from a young age and doesn't actually know much about British culture.
- In The Big Bang Theory, Raj - despite being an Indian - hates the idea of living in India. The unexpectedness of this is played for comedy, especially since he is stereotypically Indian in other ways - being a geek, believing in Hinduism, etc. For instance, in one episode Sheldon's looking for mental challenges and Raj suggests learning Hindi, only to sheepishly admit he never learned Hindi when it turns out Sheldon already did.
- In the intro fic to a Shadowrun Beginner's Box, the human character is surprised when the elf doesn't speak Sperethiel. Though, in that case it's because the language has only been around for a couple generations and was introduced by a group of separatists that her parents refused to join.
- In Persona 2 party member Lisa Silverman has two white American parents who are naturalized Japanese citizens, so you'd expect her to be fluent in English, but she can only speak Japanese and Cantonese as a result of her Otaku parents wanting her to be a traditional Yamato Nadeshiko.
- Dragon Age: Inquisition:
- Sera is an elf, but actively (and, at times, violently) shuns everything "elfy" and is terrified of anything pertaining to ancient elven history. It is a consequence of her being raised mostly by humans, with little contact with members of her own race.
- A Qunari Inquisitor will also get this reaction from The Iron Bull if they speak to him about their heritage, Bull is quite insistent than the Inquisitor is not a Qunari since they were born outside the culture and don't follow the Qun, instead they are a Vashoth (as opposed to their parents, who are Tal Vashoth since they intentionally left). Given the way the Inquisitor reacts to certain phrases Bull uses it's implied they don't really speak Qunlat either.
- Despite her blonde hair and blue eyes and western name, the half-Scottish Lily from Katawa Shoujo is Japanese through-and-through. She can barely speak a lick of English and doesn't quite like Scotland.
- Little Busters!: This is a real source of angst for Kud. She's ethnically Russian (her full first name is Kudryavka), but she grew up on a fictional Pacific island officially owned by the USSR (a clip from the anime implies she was one of few white people living there) and then spent many years travelling around the world with her Japanese grandfather; as it was always intended that she attend high school in Japan, she was taught the language from a young age. However, when she does start living in Japan full time, she finds that almost all of her peers simply treat her as a Funny Foreigner type. She tries to fulfill their expectations, but due to her Japanese upbringing and terrible English skills she can't really manage it and ends up disappointing them. (Her Russian seems to be much better, but is also apparently less 'cute.') As a result she ends up feeling very isolated, and like there's no place in the world where she actually belongs.
- Sparrow from But I'm a Cat Person is Jewish by birth but, despite the attempts by her mother, is barely connected to her heritage.
- Numbuh 1 from Codename: Kids Next Door has an English accent but is American raised. When he and his father visit England, Nigel ends up confused due to the differences in language and culture.
- Penny from Littlest Pet Shop (2012) visits other pandas in China in one episode. However, she finds out she has little in common with them. In turn, they think America is essentially how it was in Singin' in the Rain and other older film musicals.
- Miraculous Ladybug: Marinette Dupain-Cheng, who as her name suggests has Chinese ancestry, turns out to speak terrible Mandarin compared to blonde, blue-eyed Adrien Agreste. Played for comedy rather than angst or drama when a relative of Marinette's from The Old Country comes to visit and Adrien is drafted in to translate while her mother is busy elsewhere, impeded by Marinette's inability to be near Adrien without turning into a blushing, stammering and all-round adorkable mess.