The Last Lingua Franca: English Until the Return of Babel. By Nicholas Ostler. Walker & Company; 368 pages; $28. Allen Lane; £20. Buy from Amazon.com, Amazon.co.uk

ENGLISH is the most successful language in the history of the world. It is spoken on every continent, is learnt as a second language by schoolchildren and is the vehicle of science, global business and popular culture. Many think it will spread without end. But Nicholas Ostler, a scholar of the rise and fall of languages, makes a surprising prediction in his latest book: the days of English as the world's lingua-franca may be numbered.

Conquest, trade and religion were the biggest forces behind the spread of earlier lingua-francas (the author uses a hyphen to distinguish the phrase from Lingua Franca, an Italian-based trade language used during the Renaissance). A linguist of astonishing voracity, Mr Ostler plunges happily into his tales from ancient history.

The Achaemenid emperors, vanquishers of the Babylonians in 539BC, spoke Persian as their native language, but pragmatically adopted Aramaic as the world's first “interlingua”. Official long-distance communications were written in Aramaic, sent across the empire and then translated from Aramaic upon arrival. Persian itself would serve as a lingua-franca not at the time of the empire's greatest heights but roughly from 1000AD to 1800. The Turkic conquerors of Central Asia, Anatolia and the Middle East, though they adopted Islam and worshipped in Arabic, often kept Persian as the language of the court and of literature. Persian was also the court language of Turkic-ruled Mughal India when the British East India Company arrived.

Some lingua-francas have ridden trade routes, but these are tongues of convenience that change quickly with circumstances. Phoenician spread from its home in modern Lebanon along the northern coast of Africa, where (pronounced in Latin as Punic) it became the language of the Carthaginian empire. But Rome's destruction of Carthage in 146BC reduced it to a dwindling local vernacular. Greek, by contrast, planted deeper roots, surviving not only Rome's rise but also its fall, to serve as the lingua-franca of the eastern Mediterranean for over 1,000 years.

What does all this, then, have to do with English? Often very little. It seems sometimes that Mr Ostler, fascinated by ancient uses of language, wanted to write a different sort of book but was persuaded by his publisher to play up the English angle. The core arguments about the future of English come in two chapters at the end of the book. But the predictions are striking.

English is expanding as a lingua-franca but not as a mother tongue. More than 1 billion people speak English worldwide but only about 330m of them as a first language, and this population is not spreading. The future of English is in the hands of countries outside the core Anglophone group. Will they always learn English?

Mr Ostler suggests that two new factors—modern nationalism and technology—will check the spread of English. The pragmatism of the Achaemenids and Mughals is striking because no confident modern nation would today make a foreign language official. Several of Britain's ex-colonies once did so but only because English was a neutral language among competing native tongues. English has been rejected in other ex-colonies, such as Sri Lanka and Tanzania, where Anglophone elites gave way to Sinhala- and Swahili-speaking nationalists. In 1990 the Netherlands considered but rejected on nationalist grounds making English the sole language of university education.

English will fade as a lingua-franca, Mr Ostler argues, but not because some other language will take its place. No pretender is pan-regional enough, and only Africa's linguistic situation may be sufficiently fluid to have its future choices influenced by outsiders. Rather, English will have no successor because none will be needed. Technology, Mr Ostler believes, will fill the need.

This argument relies on huge advances in computer translation and speech recognition. Mr Ostler acknowledges that so far such software is a disappointment even after 50 years of intense research, and an explosion in the power of computers. But half a century, though aeons in computer time, is an instant in the sweep of language history. Mr Ostler is surely right about the nationalist limits to the spread of English as a mother-tongue. If he is right about the technology too, future generations will come to see English as something like calligraphy or Latin: prestigious and traditional, but increasingly dispensable.