Here’s my theory, tested and true: Divide your age by the number 7 and you’ll find the number of days you can spend at home with your parents before reverting to actual 7-year-old behavior. The number of days increases along with your age, but the inevitable endgame (with its attendant cookie wars and territorial tantrums) will always be there, waiting. I have yet to develop a similar formula for time spent with a sweetheart’s parents, though Julie Delpy’s second feature, 2 Days in Paris, at least suggests a starting point for further research. After two days in an apartment above her parents’ flat, the relationship between 35-year-old Marion (Delpy) and Jack (Adam Goldberg) regresses to one more typical of a couple aged approximately 17.5 years. Coincidence?

Admittedly, there are control group issues in this particular scenario: When the parents are free-wheeling Frenchies (played by Marie Pillet and Albert Delpy, Julie’s actual parents), the woman a bracing, ex-pat combination of impish and high strung, and the man a sardonic, possessive American who doesn’t speak the language, the variables are off the charts. And what makes Delpy’s magnum opus (writer, director, producer, editor, star, narrator, singer -- caterer?) more charming than perhaps it sounds on paper is her attention to the connections between the cultural, political, social and emotional nuances of those variables, and how they can conspire, rather innocently, to unhinge any alliance formed against them. Delpy manages to take some very nuance-free themes -- the relative sexual liberation of the French, the blatantly Allen-esque paranoia and hypochondria of uber-Jew Jack, Paris as romantic nirvana -- and work (or more aptly, talk) them into a chattery world of relationship growing pains not weighed down by cliché.

Subverting Paris’ dreamy reputation is key; though the locations are suitably and recognizably iconic, all of the interior and eventually even the exterior spaces inhabited by Jack and Marion are filled with clutter, clashes and noise. Hardly the serene idyll of filmic yore -- most notably circa Before Sunset, the Delpy film this one will be justly compared to -- this is a more radical Paris. An odd couple with a two-year vintage, Jack and Marion are stopping in Paris for two days after a disastrous vacation in Italy, before heading home to New York City. Seeing your partner on home turf for the first time can be like entering foreign territory, with your beloved suddenly behaving like a foreigner; for Jack that feeling must contend with the added burden of Marion’s home turf actually being foreign territory, on which she speaks a different language and must act as his translator. The taxi drivers are solicitous sexists or insufferable racists, her ribald parents, meaning well, treat Jack as more of a novelty than a guest, and Marion keeps running into her smarmy ex-boyfriends in the street.

Delpy opens and closes the film with some doleful voiceover, which appears intermittently enough throughout to be distracting rather than organic, especially considering all the talking being done onscreen. The couple have easy, if slightly over-animated chemistry; a couple of two years, Jack and Marion banter ceaselessly, as though they were in the first stages of a relationship, where every person, place and thing in view is enlisted in the frantic upkeep of their rapport, or in every insecurity-fueled accusation. And this is before things get really juvenile. There are some funny fish-out-of-water bits involving a trip to market, lunch with the family and finally a superb house party scene in which Delpy deftly captures the ebb and flow of a relaxed gathering, its lazy dips into conversation and little puddles of boredom. Playful animations are used sparingly and flash-cut montages of imagery not sparingly enough.

Delpy wrangles her metaphors without showing too much strain, and the performances are too lovely and guileless to fault. Delpy herself, beneath her safety glasses and corona of blonde frizz, is still the wistful, enigmatic beauty of hooded eye and aquiline beak; she plays the cajoling, clueless lover well, matching wits and witticisms with Goldberg, jittery and serious but never self-serious with his face-swallowing, hipster thatch, “Visit Guantanamo Bay” T-shirt and dark, Dylan sunglasses. Though the wrap-up to the film and the couple’s widening rift is decidedly bobbled with an uneasy preponderance of voice-over, it’s nice to see that even the healthiest, snappiest cynic can’t help concluding that Paris is indeed for lovers.