But the history of Esperanto has been far from smooth. The movement was divided from the start. Esperanto attracted leftists and freethinkers of various stripes—Goebbels called it “a language of Jews and communists,” not entirely inaccurately—and the majority of those people, like Zamenhof, conceived of the language as an ethical program. But many others were interested in it primarily as a linguistic novelty. French intellectuals, in particular, were put off by Zamenhof’s brotherhood-of-man effusions, as became clear at the first international congress, in 1905, which was held in Boulogne-sur-Mer.

At that time, France was still in the grip of the Dreyfus affair. A decade earlier, the French Army, trying to cover a security leak, had arrested a Jewish officer named Alfred Dreyfus, tried him for treason, and sentenced him to life imprisonment. From the beginning, it was suspected that Dreyfus had been framed, and the resulting conflict tore French society in two, exposing and fortifying a deep vein of anti-Semitism. When the Esperantists gathered for their conference, Dreyfus still had not been exonerated, and it did not help the movement’s cause that Zamenhof was Jewish. The conference committee asked to see the text of Zamenhof’s keynote address. “Through the air of our hall mysterious sounds are travelling,” he had written, “very low sounds, not perceptible by the ear, but audible to every sensitive soul: the sound of something great that is now being born.” He ended with a prayer to the spirit of brotherhood that, under the banner of Esperantism, would unite humankind: “To thee, O powerful incorporeal mystery,” etc.

A French Esperantist, a lawyer named Alfred Michaux, described the committee’s reaction: “One can hardly grasp the wonderment and scandal of these French intellectuals, with their Cartesian and rational spirit, representatives of lay universities and supporters of secular government, accustomed to and identified with freethinking and atheism, when they heard this flaming prayer.” They told Zamenhof to revise his speech and to drop the prayer. “Tearful, isolated, apprehensive, he refused to change the speech,” Schor writes, but he deleted the final stanza of the prayer, which proclaimed that Christians, Jews, and Muslims were all children of God. Meanwhile, the conference leaders were doing all they could to keep the bad news of Zamenhof’s ethnic origins out of the press. One of the organizers, Louis Émile Javal, himself a Jew, later wrote proudly that only one of the seven hundred articles about the congress mentioned that Zamenhof was Jewish.

On the surface, the congress was a great success. Almost seven hundred people attended. There were concerts and banquets. Stalls sold Esperanto-themed pencils, pens, plates, and even a liqueur—Esperantine. Zamenhof’s speech received a loud ovation. (One wonders how many people understood it.) But the occasion cannot have seemed a triumph to Zamenhof. Not only did the Congress Committee pressure him to tone down his address; it also issued a declaration that moral commitments had no bearing on Esperanto. The movement was an “endeavor to spread throughout the entire world the use of this neutral, human language,” the committee said. “All other ideals or hopes tied with Esperantism by any Esperantist is his or her purely private affair.” This was the exact opposite of what Zamenhof intended. The whole point of his Esperanto—what he called its interna ideo—was to teach the brotherhood of man.

Still, he capitulated. He could never stop his ears to the argument that his universalist values, by sounding Jewish, would put people off Esperanto—indeed, that his mere Jewishness, never mind his values, was a burden to the movement he had created. But his coöperation could not last. In the same year as the Boulogne congress, there was another spate of pogroms. Preparing his speech for the next international conference, in Geneva, in 1906, Zamenhof described the events in his home town of Białystok. “Savages with axes and iron stakes have flung themselves, like the fiercest beasts, against the quiet villagers,” he said. “They smashed the skulls and poked out the eyes of men and women, of broken old men and helpless infants!” At the conference after that, in Cambridge, in 1907, he said flatly that Esperanto would “become a school for future brotherly humanity.” In the end, he had decided that if the others wanted to regard Esperanto as a neutral business that was their private affair. Through various disputes and difficulties, backslidings and recoveries, he remained faithful to his interna ideo for the remaining years of his life.

They weren’t many. As early as his forties, he began to suffer cardiac symptoms. He died, of heart failure, in 1917, at the age of fifty-seven. It is good that he quit the scene early. Zamenhof was exactly the kind of person that the Third Reich would set itself to eliminate. And by dying before they took over he also spared himself the experience of seeing his children die. His son was shot by the Nazis in 1940. Both of his daughters were sent to Treblinka and did not return.

The story of Ludovik Zamenhof and the language he invented occupies the first third of Schor’s book, and it is by far the best part. That the rest falls flatter is not really Schor’s fault. “For sheer dirtiness of fighting the feuds between the inventors of various of the international languages would take some beating,” George Orwell once wrote. His Aunt Nellie had a lover who headed the Esperanto movement for some years in the twenties and thirties, and Orwell spent a lot of time with them in Paris during that period. Dirty fighting, if prolonged, does not necessarily make for good reading. Of course, there was fighting in Esperanto’s early years, too. What could be more distasteful than the French Esperantists’ treatment of Zamenhof’s Jewishness? But that whole thing reads like a novel, at least in Schor’s hands—she is a lively writer—and Zamenhof is a real hero, whom she clearly loves. By contrast, many of the people who came after him were the sort of nasty little demagogues whom one tends to find battling one another to the death for control over small, marginal movements, often on the left. Esperanto saw no end of sects, schisms, secessions, coups. Members set up rival languages: Ido, Arulo (later renamed Gloro), Poliespo. These sound like something out of “Gulliver’s Travels.”

When the Esperantists weren’t attacking one another, they were being attacked from the outside. Zamenhof had hoped that the United States would become the headquarters of Esperanto. This made sense to him: America was already multiethnic. There the Esperantists would not have to fight tribalism the way they had to in Europe. But that was part of the problem: many Americans felt that they were multiethnic enough, thank you. Many were also perfectly happy to embrace nationalism, as they are today. So, between the two World Wars, most Esperantists remained in Central Europe and the U.S.S.R. (also in Japan). There, though they were steadily persecuted, their movement managed to survive. Indeed, this period seems to have been the high-water mark of Esperanto, though, even then, its principles were so contested and revised that it’s hard, at times, to figure out which version of Esperanto Schor is talking about.