You know that French saying, je ne sais quoi? Which literally translates to “I don’t know what,” but is used to describe an ineffably unique quality, like the one that new velvet chaise imparts to your bordello-themed parlor? Say it in Paris, and you might as well be wearing a beret and lunching at the Hemingway cafe — because it’s something employed mostly by Americans, and rarely the French. Quelle surprise, non?

John von Sothen’s memoir of Parisian expat life, “Monsieur Mediocre: One American Learns the High Art of Everyday French,” offers dozens of these inside-baseball insights into a place that continues to mystify and enchant, what with its manicured gardens where slim sophisticates and impeccably behaved children gorge on all the brie, Bordeaux and free health care they can manage. After 15 years as a Parisian, von Sothen has a decidedly less Disney take on his “cold and cynical” town, where he moved with the French girlfriend he met in a Brooklyn cafe (and following a childhood charmed by his mom’s tales of years spent as an artist in Paris).

Von Sothen had his own preconceptions before the move — that he would live in a 19th-century apartment with a quintessentially Parisian Haussmannian facade, near a park “where you can sit underneath a two-hundred-year-old willow, not realizing your bench was actually a sculpture by Rodin.” His pregnant girlfriend would give birth “in a hospital steps from the Seine” featuring “nurses in white headscarves” and “mahogany-trimmed halls.” Instead, his daughter was born in the suburbs, “a French Scottsdale, Arizona,” and he moved into a warehouse-style loft in the 10th arrondissement — a trendy neighborhood that would be the target of a 2015 terrorist attack and the site of squalid migrant tent cities a year later. Not exactly the whimsy-drenched milieu of “Amelie.”

Then again, von Sothen is hardly roughing it. Though he’s a freelance writer who shares two kids with his theater actress wife — and despite the fact that both families boast aristocratic backgrounds, which von Sothen seems mildly obsessed with — it remains annoyingly unclear how he affords the country house near Normandy, the membership to the chichi “pony club,” the urban square footage that inspires a neighborhood kid to ask how he “became a millionaire,” and the weeks-long vacations to Italy. Of course, that’s not the point — if you never got past how Rachel and Monica paid for their apartment in “Friends,” you probably missed all of Chandler’s wisecracks. And in any case, von Sothen offers some delicious, uniquely French details about all those tony trappings, like the rural electricians who promised to show up to the country house only “ ‘aux beaux jours’ (when it’s nice out)”; or his fellow Parisians’ manic obsession with planning city-fleeing vacations months in advance: “It’s almost as if they chant the New Year’s countdown 4-3-2-1 and start to look at farmhouses in Provence as the champagne pops.” (Skip the planning, and you might be stuck — quelle horreur! — in a tourist-overrun Paris in August, when the Left Bank “becomes an annexed protectorate of Wichita, Kansas,” von Sothen writes. “Something dark happens to you. You die a bit inside, and you simulate. . .what life would be like following a biological attack.”)

One such vacation, which von Sothen took to Umbria for two weeks with his wife, daughter and several other couples provides fodder for an especially amusing essay on the French tradition of “vacationing en groupe.” He finds himself woefully unprepared for the sprint to claim the best bedrooms; the varied liberal-artsy workshops, or “ateliers,” that each vacationer is expected to plan and lead; the insistence on incessant, full-participation group activities (“I’m not sure if it’s the ingrained notion of République they learn at school or if it comes from the socialist colonie de vacances (summer camps) they attend as children in July. . .but the more my housemates wanted to be together, the more I wanted to be alone, and by the second week, the impromptu atelier I’d created could have been called Find the hiding John”); and the near-militant devotion to planning, sourcing and preparing exquisite spreads for every meal. “For the French,” von Sothen explains, “the first twenty-four hours of vacation are reserved for the food shop” with “five or six adults cramming into a small car. . .why else would you to go Umbria if not to drive around in a clown car looking for tuna?”

Food, it turns out, is as beloved and belabored in France as we imagine it to be. French dinner parties, as von Sothen describes them, are so precisely, elegantly choreographed — down to the trou normand, a smoke-and-drink break between the second and third course — that von Sothen’s American sensibilities finally tire of the whole to-do and he starts inviting friends instead to after-work drinks, “a time-honored American tradition of keeping friends without having to go all in.” But “these invites routinely fell flat, often met with the response, ‘But John, what will we eat?’. . .For my French friends, a drink without eating is something close to heresy.”

Von Sothen offers some incisive takes on French politics — it’s especially disquieting to hear an expat’s view of the Front National party’s near-win in the wake of President Trump’s election; as well as on raising kids in a country where, he jokes, “the only thing they make better than wine is children.” Occasional flashes of snootiness — like the description of suburban horse-riding lessons as “babysitters, time outs, and cocktail parties for millions of French parents”; or paragraphs of sincere, impassioned complaining about weekend traffic to and from his country house, which, he can’t help but mention, “is older than the Declaration of Independence, but I rarely think of it that way, until of course I try to heat it in the winter” — read as more than a little tone deaf, much like one of those “Reebok-wearing tourists looking for the Lou-vray.” Then again — what’s a book about the French without a little well-meaning snobbery?

Rachel Rosenblit is a freelance writer and editor in New York.

Monsieur Mediocre

One American Learns the High Art of Everyday French

By John von Sothen

Viking. 288 pp. $25