French comedies generally haven’t traveled well in terms of Hollywood remakes, and “The Big Wedding” is no exception to the rule. It’s based on Jean-Stephane Bron’s 2006 “Mon frère se marie,” and despite a strong ensemble cast Justin Zackham’s redo has about as much distinction as its blander-than-bland title.

Bron’s original was about the upcoming nuptials of a Vietnamese boy who’d been adopted by a Swiss couple. The arrival of his traditionalist biological mother and uncle required his dysfunctional family to strive to pretend amity for the duration. Zackham changes the setting to the US, and turns the Vietnamese lad into a Colombian. His mother is a hard-lined Catholic, and the local parish priest, despite some personal quirks, is equally so. Many other complications ensue, which turn the story into an extended sitcom with a particularly raunchy streak that grows more and more artificial and hard to stomach as it proceeds.

The kernel of the Bron/Zackham premise derives from “La Cage aux Folles,” and it’s really no more reasonable this time around. Alejandro (Ben Barnes) is marrying Missy (Amanda Seyfried), daughter of Muffin (Christine Ebersole) and Barry (David Rasche). Fearful of what his mother Madonna (Patricia Rae) will think of his adoptive parents Don (Roberto De Niro) and Ellie (Diane Keaton) being divorced, he asks them to pretend still to be happily married. Unfortunately that will freeze our Bebe (Susan Sarandon), Don’s long-time live-in girlfriend (and Ellie’s onetime best friend), who also happens to be catering the wedding party.

Then there are Alejandro’s siblings, Lyla (Katherine Heigl) and Jared (Topher Grace). She’s estranged from her father and separated from her husband. And when she visits her brother, a doctor, at the hospital where he works, she faints at the sight of the newborns—which signals something immediately to the audience, though Doc Jared, slow on the uptake, won’t understand the significance until way down the line. Jared, meanwhile, has been turning down women’s approaches until he finds his authentic soul mate. But when Madonna shows up with her beautiful daughter Nuria (Ana Ayora), however, he’s instantly smitten, and the girl seems ready to party.

The final figure in the equation is Father Monighan (Robin Williams), the parish priest who’s to perform the ceremony, and who reads the young couple the riot act during their pre-nuptial conference.

With an ensemble like this, one would expect some laughs—and a bit of depth. Unfortunately, you get very little of either. Zackham’s default setting is sexual naughtiness (nothing too steamy, but a lot of slapstick in the sack and out), and always at embarrassing moments. Worse, the script doesn’t lend any consistency to the characters, who abruptly change from moment to moment for the sake of some cheap laugh. Even in farce a character needs a basic grounding to function effectively within a plot, however intricate it might be. Here, though, the characters are mere pawns who will be at odds one moment and in bed the next (or drunk and then suddenly sober, irate and then abruptly calm), to serve the needs of the script. The result by the close—which itself brings some truly weird, incredible revelations—is that the story has lost the most elementary basis in realism, which even a sitcom needs.

Still, the cast do try hard, as embarrassing as some of the stuff they have to do might be. Among the leads De Niro and Keaton are worst used, though they’re certainly game, while Sarandon is stuck with the more serious, sentimental stuff. Among those in support, you most pity Heigl and Grace, while Williams tries to get by through underplaying (not very successfully, his character being so poorly written). But even he is better off than Barnes, since Alejandro (like the son in “La Cage”) is basically a jerk, or Rasche and Ebersole, who as the prospective in-laws are compelled to act like a couple of nitwits. (The jokes about Muffin’s cosmetic surgery are particularly crude.) On the visual side, the picture is bright and classy, with an agreeable production design (Andrew Jackness), elegant costume design (Aude Bronson-Howard) and lush cinematography (Jonathan Brown).

Undemanding viewers of mediocre network sitcoms might enjoy “The Big Wedding,” which is about on a par with them. But in the end it’s as synthetic as the script tells us Muffin’s face has been rendered by constant nipping and tucking, and feels especially noxious because of all the acting talent it wastes.