In China last month, Theresa May attended the launch of the British Council’s English is Great campaign, intended to boost interest and fluency in our national language. This might sound like Donald Trump’s notorious “Make America great again”, but comes in fact from a stronger position. Beyond doubt, the use of English is greater than ever, and far more widespread than any other language in the world. All non-English-speaking powers of our globalised world recognise it as the first foreign language to learn; it is also, uniquely, in practical use worldwide. The British Council reckons that English is spoken at a useful level by some 1.75 billion people, a quarter of the world’s population. It is taught from primary level up in all China’s schools; it is the working language of the whole European Union.

On the news service France 24, English is used more prominently than French. Its use is required of all airline pilots and control towers, 24/7. And it is seen as an essential cachet for progress in some amazing places: for example, 14 years ago, the prime minister of Mongolia – a country with no historic links to an English-speaking power – decreed it should replace Russian in all schools as part of his aspiration to make Ulaanbaatar a centre for telephone call services. One in six Russians claims to speak it. English is clearly the language of choice for those with global aspirations, whatever their political stance towards Anglo-Saxon powers.

This global acceptance of English, now far beyond the zones of influence of the British empire or the United States’ backyard, has effectively grown up in just a century – neatly, and a little paradoxically, since the 1919 treaty of Versailles. In deference to the US, this was the first international treaty written in English; but it also turned out to mark the incipient decline of the world’s greatest English-speaking institution, the British empire. From a language point of view, however, British power had the good fortune to be succeeded by its cousin in North America, so that the usual historic lag, as political command leads on to linguistic imitation, was disguised. Even as Britain began to decline economically, its established position was reflected by increased take-up of English as the language to learn.

But all this while, especially from the 1920s to the 1990s, the focus of US expansion was changing, moving from North America to the world, leading to influence on trade, engineering, telecommunications, mining, media, science and finance, as the dollar moved to replace sterling as the world’s reserve currency. This was followed by the digital information revolution, creating new fortunes based in Silicon Valley at the turn of the 21st century. These were all positive for the world role of English (a role founded by Great Britain), but should have been expected to peak later, in the growth of soft power and the increased popularity of American culture.

When circumstances change, dominant languages fall. And the change is clearly coming

It is this lagged growth of English, reflecting US influence hitherto, that we are now experiencing. Yet it is happening in a 21st century when other nations, particularly in Asia but also in South America and Africa, are far outpacing the US (let alone Britain and the European Union) in economic growth rates. This is an amazing juncture in world history. And two questions arise. Is the position of English a real asset to the states that speak it natively? And is the language likely to hold this position in the pecking order indefinitely?

Considering the windfall benefits of English as one’s own language, some immediate advantages are undeniable. It has given direct access to the world’s principal medium of communication: good for having an inside track on “news we can use”, as well as facilitated access for well-educated anglophones to influential jobs. It has also put us in a position to charge some kind of rent for allowing others admission to this linguistic elite: hence the massive earnings from teaching English as a foreign language (now well over £2bn in the UK alone, reaching £3bn by 2020), and global markets for English-language publishing (£1.4bn in exports in 2015). This is another spin-off from Britain’s recent history of dominance, like the siting of the Greenwich meridian, giving daily opportunities for global trades between Asia and America, or the association of investment, and hence global finance, with the City of London.

But special knowledge of a language is an asset that wastes all too soon when it becomes global property. World English will have just a historic connection to Britain or the US, and knowing it well is no longer exclusive to native speakers. Even the short-term windfall advantages came with a moral hazard. Presumption of entitlement can breed complacency at home, as well as resentment abroad – all too evident in the current “negotiations” on Britain’s divorce from Europe.

It is hard to credit the vulnerability of a language such as English – which has spread, unbidden and unplanned, far beyond its homeland, and is even claimed to be the “language of freedom”. But this in itself is nothing new. Transnational lingua francas, once established, always give off an aura of permanence. Yet when circumstances change, they fall. And the change is clearly coming.

And so the natural expectation will be that after the new powers, such as China, India or Brazil, establish themselves economically, politically (and probably militarily), their linguistic and cultural influence too will come to be felt, among those who want to do business with them, and then with one another. But as with all newly dominant languages, there will be a lag.

If centred on China, say, the world may be less enthusiastic for “the hidden hand” of Adam Smith’s free markets. If other centres emerge, the result may be more mixed, asserting local Islamic, Buddhist or Hindu traditions. Evolving translation technologies may make languages largely interchangeable, pushing national cultures into the background. Whatever, there will be no special deference to the current English-speaking tradition.

Something like this, after all, is what happened in the 17th century, when the newly global power France won a role for French as a common language for civilised Europe: French – with strong Enlightenment overtones – replaced Latin itself, which had held that role for 15 centuries. In a different way, it is what happened in the 19th century, when the imperial interlopers Russia and Britain abolished Farsi in their Asian domains. Before that, Farsi had been pre-eminent for 800 years as the language of Muslim culture, trade and politics.

For English, therefore, its current peak is likely to be as good as it will ever get, its glory as a world language lasting just a couple of centuries – almost a flash in the pan, not yet comparable with those forerunners Latin or Farsi. And on present form, its fall is likely to coincide with the latest rise of China, whose documented history has run for three millennia. Chinese, too, is great.

• Nicholas Ostler is the author of Empires of the Word, and The Last Lingua Franca. He chairs the Foundation for Endangered Languages