The time has come to retire the phrase “inspired by true events” as an introductory subtitle for narrative films. Given the level of invention that enters into any work of art, whether it be a trompe-l’œil painting or an on-the-ground documentary, an avowal of factual intent often comes across as protesting too much.

Take the new film “Persian Lessons.” The picture is based on “Erfindung einer Sprache,” a short story by the late German screenwriter and director Wolfgang Kohlhaase. When queried about the source material for the film, director Vadim Perelman cites Kohlhasse’s work of fiction, but also notes that the picture is less about specific individuals than a type of individual, a person who survives dire circumstances through “wit and smart thinking.”

“Inspired by,” in so many words, nods toward verisimilitude even as it allows for wiggle room. Given that the milieu for “Persian Lessons” is the Holocaust, perhaps Mr. Perelman and screenwriter Ilya Zofin wanted to fend off potential complaints about playing fast-and-loose with history. Certainly, artists who engage with historical circumstances that are of some consequence had better get their ducks in a row.

All of which is a roundabout way of wondering whether “Persian Lessons” might not strain the limits of both credibility and metaphor. Mr. Perelman, likely best known on these shores for “Sand and Fog” (2003),  has crafted an ingenious picture. Its main storyline is deftly introduced, tensely elaborated upon, and brought to an almost Zen-like resolution. Still, this solid movie is, in the end, oddly unsatisfying, being a showpiece whose bravura denudes it of moral currency.

The film begins with Nazis rounding up Jews in occupied France circa 1942. A wiry young man named Gilles (the Argentinian actor Nahuel Pérez Biscayart) is among those herded onto the back of a truck for a destination unknown but a fate guessed at by all. The man huddled next to Gilles offers a valuable book as barter for the sandwich Gilles has squirreled away in the pocket of his overcoat. The inside of the book is inscribed in Farsi. This chance encounter provides the seed of an idea by which Gilles hopes to evade certain death.

He does so by claiming that he is not Jewish but, in fact, Persian. The guards responsible for the execution of their prisoners, hearing this news, hold their guns. The commanding officer, Klaus Koch (Lars Eidinger), is on the lookout for a Persian. A peculiar request, you might think, and you wouldn’t be wrong. Koch is a former chef who dreams of opening a restaurant at Tehran upon the Third Reich achieving world dominion. Shouldn’t take but a year or two, by his calculations, and he wants Gilles to teach him the language.

Whereupon Gilles and Koch play an extended game of cat-and-mouse. Gilles, the rabbi’s son who doesn’t know a lick of Farsi, begins inventing words to teach his keeper. The trouble is that Gilles has to retain the nonsense words — invented, in large part, from the names of those interned with him — in order to sustain the ruse. There will be more than hell to pay should Koch learn the truth about the Persian on which he becomes increasingly dependent.

Mr. Perelman’s picture suffers from some fairly tenuous plot points — Koch’s acceptance of Gilles’ mixed-race heritage is too convenient by half — and a floundering side story about the romantic intrigues amongst the camp staff. Although Mr. Zofin’s script does hint at the guilt Gilles feels as his deception spares him the fates of his comrades, the tit-for-tat nature of the story doesn’t altogether suit the gravity of its context.

“Persian Lessons” is no mean entertainment — it is, in fact, quite gripping — but one’s disbelief is tested more than is ideal for a movie that takes on quite as much as this one.