It’s a pertinent issue in Hong Kong, where there is pressure on both children and adults – local and expat – to speak more than one language. Native Cantonese speakers attended schools where the medium of instruction was English before the 1997 handover from Britain to China, and now Mandarin is emphasised. Expatriate children in international schools are also increasingly taking Mandarin classes.

Research has shown that babies who live in bilingual environments can distinguish between two languages by reading lip movements and facial expressions, and they show a strong preference for the language their mother spoke during pregnancy.

Speaking more than one language is seen as a good thing – and not just so that we can order two beers and a pizza in Italian, Chinese or French. Many parents encourage their children to learn a second language at school, possibly even a third, but – beyond that acquiring a foreign language forms a mandatory part of most school curricula – do we know why we are doing it or whether it has any long-term value?

“Social-emotional development can be enhanced, if the communications have salience,” Mattoli says. There is evidence that more and more employers want languages and cultural skills, and the international savvy that language learning brings.

And that is important, as Mattoli observes. “Learning a language just for the sake of learning a language can be overwhelming, not to say dry, academic and apparently pointless if you aren’t actually going to use it in real life.

“It can take more time for productive speech to appear in some individuals due to the need for more processing to lock in the rules of each language, but provided the language is in a pure form and has salience (parent or significant caretaker communicates in a single language consistently), two, sometimes more, languages can be locked in at a relatively early age,” she says.

This is why children who grow up in homes where more than one language is spoken appear so fluid.

Do younger children learn languages faster? No, says Virginia Rojas, an international language education consultant. That’s a myth, she says, and there are lots of them about language.

Younger learners certainly, she says, are often able to pronounce a new language with little or no accent, and they benefit from a lack of inhibition, which means they’re prepared to take risks, have a go. And those age characteristics mean they are good language acquirers because, Mattoli says, “young children are developmentally doing multiple things already by moving through the normal developmental milestones”.

But older students are more efficient language learners, Rojas insists, “because they are cognitively mature in their own language”.

Narly Golestani, a professor at the Brain and Language Lab in Geneva, Switzerland, says there are probably two time windows when language learning is easier. “One around the age of five [when learning to write often starts] and one around the age of 12. So learning these languages later than these periods will be much more difficult,” he says.

But could learning a second, third and even fourth language do more than promote prospects post-education? Absolutely, insists the UK Subject Centre for Languages, which says it has identified as many as 700 reasons to study a foreign language.

With specific regard to schoolchildren, though, a pertinent question could be: does studying a second language promote academic ability, or hamper it by confusing children? Up until the 1950s, it was believed that raising children to be bilingual could inhibit their language development. Today’s thinking could not be more different: the Student Loans Company (which forms part of Britain’s University of Southampton) believes that an additional language enhances academics because it brings into context many other subjects: history, politics, geography, and opens doors to foreign literature.

Golestani agrees: “There’s some evidence that learning several languages, in childhood, has advantages in other domains of functioning: it can lead to better executive skills more generally, and to better working memory skills.”

Can learning another language ever be a bad thing? “It can be bad for children who are dyslexic,” Golestani says. “It can tax them, and make it hard for them to do well even in their native language, and also for children who are at the low end of a ‘continuum’ in terms of potential for language learning.”

Mattoli also says it’s important not to overload young children with too much language learning. “The brain only has the ability to learn so much at once; making new neural connections takes a lot of work, resources and energy, and if it is being taxed with seemingly non-useful tasks, such as learning a third or fourth language that is not naturally used in daily communications, it is not likely that it will be able to do some other necessary developmental tasks as efficiently,” she says.

On balance though, a second language is good for the brain.

Alcohol can help you speak a foreign language more fluently, study shows

Learning a second language “boosts” brainpower, concluded a University College of London team, who found that learning another language altered grey matter – the area of the brain that processes information – in the same way that physical exercise builds muscles. (Confirmation of the link between brain use and robustness came from a study of London taxi drivers, who prove to have a larger than average hippocampus, the part of the brain associated with navigation.)

And those people who learned a second language at a young age were more likely to have more advanced grey matter than those who learned one later.

It is that build-up of cerebral muscle that could help to protect the brain from the effects of ageing. Research at York University in Toronto, Canada, found that bilingual people are much better at retaining their mental abilities into old age than those who speak only one language. A well-developed brain – it seems – is less quickly broken down by degenerative disease.

So it would appear that the benefits of a second – and third or even fourth – language are manifest throughout life: they support academics, enhance career opportunities, make travelling fun and sustain us into old age.

Fascinating language facts

There are 13 languages that are spoken by more than 100 million people. These are: Mandarin, English, Hindi, Spanish, Russian, Arabic, Bengali, Portuguese, Malay-Indonesian, French, Japanese, German and Urdu. Of these, the most widely spoken are Mandarin, English, Spanish, Arabic and Hindi.

There are roughly 6,500 spoken languages in the world. However, about 2,000 of those languages have fewer than 1,000 speakers.

We are all designed to acquire language, but we are built to learn and accommodate more than just one: monolinguals are effectively underusing abilities by not tapping that potential.

The most prolific language speaker on record is Emil Krebs (1867-1930), a German who mastered 68 languages and studied a further 120.

Interestingly, bilinguals don’t necessarily “think” in any language, while performing tasks such as walking or taking a bus, says Francois Grosjean, author of Bilingual Life and Reality. Thought can be “visual-spatial and non-linguistic. It is only when planning to speak that individual languages intervene”, he writes.