There is a stark north-south divide in whether young people in England are learning modern languages, an annual survey from the British Council says.
In some London boroughs, 75% of pupils take a language GCSE, while in authorities such as Middlesbrough and Blackpool it is below 30%.
The survey also suggests that this languages gap is getting even wider.
The British Council says the lack of language skills is costing the UK "tens of billions in missed trade".
There have been repeated warnings about declines in language learning, but this year's Languages Trends Survey suggests significant regional differences.
On average, across inner London boroughs 65% of young people take a language GCSE - but across authorities in north-east England it is 43%, it says.
The highest levels of language learning in England are in inner and outer London and the South East - while the lowest levels are in the North East and Yorkshire and the Humber.
And Blackpool in the North West and Sandwell in the West Midlands have among the lowest individual rates for taking GCSEs.
The overall national picture suggests numbers taking languages at GCSE have "stabilised" at about 50%, bolstered by the requirement to study a language as part of the English Baccalaureate performance measure.
But provisional figures for this summer's exam entries, published by Ofqual on Thursday, show slight annual falls in French, German and Spanish.
The British Council highlights a substantial long-term fall for languages at A-level, with numbers taking French having declined by a third since the mid-1990s,
The council has warned of the economic damage from poor language skills - and that young people without access to languages are missing out on skills that would improve their employability.
Research for the government's trade and investment agency, carried out by Prof James Foreman-Peck, found that a lack of language skills lost the UK economy an estimated £48bn every year.
The report says that UK businesses could improve trade opportunities with better language skills.
"Not only are the personal benefits of learning a language huge, but the country's current shortage of language skills is already estimated to be costing the economy tens of billions in missed trade and business opportunities every year," said Vicky Gough, the British Council's school adviser.
"If we are to ensure that the UK remains globally competitive in the current and ever-changing landscape, we need all of our young people to be given the chance to acquire these vital skills."
A Department for Education spokeswoman said: "The introduction of languages as a compulsory part of the primary curriculum and, more importantly, the EBacc at GCSE level, has begun to reverse the decline in modern foreign languages."