In a rich new play by Sanaz Toossi, four Iranians and their language teacher find second selves in a second tongue.If you’ve ever tried, as an adult, to learn a new language, you know how painful it can be; it’s bad enough to hear yourself mangling Italian, but worse to hear it mangling you. For those of us accustomed to sounding sharp with our words, it can come as quite a blow to discover the shabby figure we cut in the ill-fitting suit of someone else’s.How our mother tongue gives us voice yet limits our world — and how a new tongue expands that world yet may strangle our voice — is the subject of “English,” a rich new play by Sanaz Toossi that opened on Tuesday at the Linda Gross Theater. Both contemplative and comic, it nails every opportunity for big laughs as its English-learning characters struggle with accents and idioms. But the laughter provides cover for the deeper idea that their struggle is not just linguistic.The play, a coproduction of the Atlantic and Roundabout theater companies, is after all set in Iran in 2008, against a backdrop of travel restrictions and family separations. Each of the four students prepping for the Test of English as a Foreign Language, or Toefl, at a storefront school in Karaj, a city of two million not far from Tehran, has a different reason for enrolling.For the cheerful 18-year-old Goli (Ava Lalezarzadeh), the promise and pleasure of new opportunity is reason enough. “English is the rice,” she explains in the inadvertent poetry of the partially fluent. “You take some rice, and you make the rice whatever you want.”But the others are more ambivalent. Dignified Roya (Pooya Mohseni) is there only because her son, who lives in “the Canada” with his wife and daughter, has insisted she speak English if she wants to live with them. He will not have his daughter’s assimilation threatened, he has warned, by a grandmother cooing in Farsi.If Roya is angry about this situation, she mostly suppresses the feeling, leaving her son hilariously passive-aggressive voice mail messages in which she offers evidence of her growing fluency. “I know all the numbers now,” she tells him. “Forty-three. Five hundred and thirty-eight. And seven.”But for Elham (Tala Ashe), anxiety is upfront: Having failed the Toefl five times, she must pass it if she wants her provisional acceptance at an Australian medical school to become official. When the Toefl teacher, Marjan (Marjan Neshat), tells her that “English isn’t your enemy,” she answers, “It is feeling like yes.” Her accent, she adds, is “a war crime.”Marjan learned English during nine years spent living in Manchester, England, gradually experiencing the way the fog of alienation can give way, through language, to the thrill of connection. Now that she is back in Iran, though, her English is eroding at the edges, at least in comparison to that of the fourth student, Omid (Hadi Tabbal), whose accent is minimal and vocabulary exceptional. Playing a game in which everyone must name items of clothing as quickly as possible while tossing a ball, he wins handily, wowing the others with “windbreaker.”Tabbal, left, plays the standout student in the English class taught by Neshat’s character. We understand her fluency (nine years in Britain), but there’s a mystery behind his (where did he learn the word “windbreaker”?).Sara Krulwich/The New York TimesOver the course of 22 scenes representing lessons, office hours and smoke breaks during the six-week course, we get to know all five characters well, and yet they also remain as stubbornly enigmatic as people do in real life. Their progress, too, is unpredictable, their skills sometimes stalling, then bounding forward, with new words and seemingly new ideas emerging.Not that we are told this; we just see it happen, thanks to Toossi’s clever theatricalization of the process. (When the characters speak English, they do so haltingly and with an accent; when they speak Farsi, which we hear in English, it’s swift and unaccented.) Even Elham, her W’s no longer sounding like V’s, and her tempo improved from largo to allegretto, is eventually able to pose a challenge to Omid’s fluency.The mystery of that fluency (why does he know “windbreaker”?) is one of the more obvious tensioning devices in a play that, despite its pleasures — but also at the root of them — has a somewhat schematic structure. Like a lifeboat movie, it features the immediate and broad differentiation of characters, their shifting alliances in the face of a looming threat and an eventual resolution involving the revelation of lies and someone cast overboard.Nor are its themes entirely novel; the drama of superimposing one language on another is at the heart of works as widely varied as Brian Friel’s “Translations” (in which a 19th-century cartographer is charged with rendering Irish place names in English) and the hyper-asterisked Leo Rosten novel “The Education of H*Y*M*A*N K*A*P*L*A*N,” set among immigrants in a night school English class and turned into a musical in 1968.But the delicacy of Toossi’s development handily makes up for both problems, especially the hysteria of lifeboat melodrama; in a recent interview in The New York Times, she told my colleague Alexis Soloski that “writing a trauma play makes me want to dry heave.”So in dealing with characters who could easily be exoticized in their chadors, Toossi has chosen instead to focus on their familiarity; like most of us, they deal less with the disaster of geopolitics than with an atmosphere of mild if daily discomfort. As such, the insights here are deep but never shattering, as when Roya perceives the crucial distinction between the verbs “visit” and “live” in one of her son’s messages. If the world’s happiness does not depend on it, a grandmother’s does.The director Knud Adams gently underlines the calm, almost classical rhythms of Toossi’s writing. Chopinesque piano solos play between scenes. As the play contemplates the question of language from several angles, the cube-like set, by Marsha Ginsberg, slowly rotates, offering in turn a street view of the building, the classroom interior and an entry portico. The cast is uniformly excellent, in a suitably unshowy but fully lived-in way.Too much delicacy has a way of wearing thin, though; with its refusal of trauma and even climax — the romance, if there is one, is buried — “English” begins to feel a bit overlong despite its moderate running time of an hour and 45 minutes.Still, the longueurs are worth it, forcing the audience into a useful position of slight non-fluency. We don’t always know what is going on in the play, as we don’t in the world either. And as each character struggles to decide whether to become another person by mastering another language, we are asked to consider whether we in the English-speaking West are not just cultural imperialists but linguistic ones as well. And whether, perhaps, those are really the same thing.EnglishThrough March 13 at the Linda Gross Theater, Manhattan; atlantictheater.org. Running time: 1 hour 40 minutes. More