Translating the Danish word “festen” is easy. It means “the celebration.”

Translating the U.K. legit hit “Festen” into a commercial success on Broadway, however, may prove a bit more challenging.

The play originated at the Almeida in London in 2004, transferred to the West End for a rapturously received run and is currently touring the U.K. The U.S. incarnation opens at the Music Box April 9.

But big biz in Blighty doesn’t always travel well across the Atlantic.

“Festen,” after all, is still a new straight play on Broadway, written by a little-known British playwright, with a foreign word for a title.

David Eldridge based his script on a 1998 Dogma 95 film directed by Danish helmer Thomas Vinterberg. The play follows the story of the film faithfully, eavesdropping on a well-heeled Danish family gathered for a social occasion that goes wrong when the golden-boy son’s toast reveals dark secrets from the past.

Many movie buffs know the film and love it, but the stage adaptation’s title won’t help much with brand recognition in the States: Although the pic is called “Festen” in the U.K., its American title is “The Celebration.”

Rather than bring over British actors (like fellow April opener “The History Boys”), Broadway’s “Festen” has enlisted a 14-person cast of Americans that includes Julianna Margulies (“ER”), Jeremy Sisto (“Six Feet Under”), Larry Bryggman (“Proof”) and, in her Broadway debut, Ali MacGraw.

Sometimes such a cast switchup can throw off a Brit hit’s mojo. Most recently, Michael Frayn’s “Democracy” boomed in London but, when it reached Broadway last season with a Yank cast, was widely considered a disappointment and never found a sizeable aud.

” ‘Festen’ is set in Denmark, but the translation was done by an English writer, and it’s being done in New York with American actors,” says Scottish director Rufus Norris, who also helmed the British production. “It’s a balance we’re trying to find.”

And full translation is exactly what the “Festen” creative team is shooting for.

“To spend $2 million putting on a play about this subject matter, with a cast that is at least twice as big as you would normally like to put on, is a very risky proposition,” Norris says. “It’s not going to work on this kind of scale unless you bring it home.”

Hence the American cast.

Bill Kenwright, the London-based producer (“Blood Brothers,” “Primo”) bringing “Festen” over with co-producer Marla Rubin, knows stars are good for B.O. — “I love ’em, if they’re right for the role,” he says — but insists there’s no stunt casting here.

Not even with MacGraw, who rarely works these days and has never done theater. Kenwright is a longtime acquaintance. “I have been trying to get her onstage for 20 years,” he says.

Other cast members may not be Hollywood A-listers a la Julia Roberts, but associate producer Dante Di Loreto sees the TV thesps (Margulies, Sisto) and Broadway vets (Bryggman, Michael Hayden) as draws.

“They’re a group of actors who are familiar enough to the audience that you want to see why those people would come together to do a play,” he says.

As for the show’s title, they talked about changing it to reflect the movie’s American name, but decided against it. “The name ‘The Celebration’ can be misleadingly frothy for a play where we are spying on a family during their most dramatic moments,” Di Loreto says.

In addition to the obvious inclusion of glowing quotes from British reviews, advertising for the Broadway run has pitched the show as a mystery, using a central keyhole motif to entice with the hint of voyeurism. Copy on the marquee asks, “Do you want to know a secret?”

Marketing targets not only regular theatergoers but also a younger crowd. Some seats at every performance will be priced at $30 for the under-30 set, and reduced pricing for mezzanine seats has been expanded.

Meanwhile, the creative team is tweaking the play’s language during the preview period, eliminating words that seem distractingly British and deciding whether bits of Stateside argot, like “dude,” have a place in the play’s world.

“We speak the same language, but we’re very different places, aren’t we?” says Kenwright of New York and London. “But something about ‘Festen’ seems so across-the-board.”

“It’s just a family having a meal where something goes terribly awry,” Norris says of the storyline. “Everybody understands that.”