Tough foreign language exams are putting students off to the extent that A-Level courses are becoming "financially unviable" for some state schools, a new report claims.
Teachers have "deep concerns" about language learning in England's schools, the Language Trends Survey 2016 claims.
A "deeply demotivating" situation has been created for pupils and teachers by factors including "harsh and inconsistent" marking and the prioritisation of maths and science subjects, according to the report by the British Council and Education Development Trust.
The report's co-author, Teresa Tinsley, said: "Languages are already one of the harder GCSEs and teachers fear that with the new exams it will be even tougher for pupils to get a good grade.
"Combine this with the expectation that a wider range of pupils will be sitting the exam and it is not surprising that teachers feel embattled.
"Improving their morale and confidence in the exam system is crucial if languages are to thrive in our schools."
The report claims that teachers in both state and independent schools do not have confidence in new A-Levels to halt a decline in the number of teenagers taking the language courses.
Now in its 14th year it claims that since the survey was launched in 2002, entries for A-level French have declined by around a third, and for German by almost half, with an increase in those studying Spanish not making up for the deficit.
Mark Herbert, head of schools programmes at the British Council, said: "The country's current shortage of language skills is estimated to be costing the economy tens of billions in missed trade and business opportunities every year. More than that, the benefits of learning a language are huge - from boosting job prospects to acquiring the ability to understand and better connect with another culture."
The gloom amid languages at secondary and tertiary level was in contrast with positive finding about language teaching in primary schools, with 42% reporting an increase in resources available.
Entries for GCSEs in modern foreign languages plummeted last year, sparking fresh concerns that the UK is at risk of falling behind on the world stage.
French, German and Spanish - which has bucked the trend in recent years - all saw drops in numbers, according to national figures published by the Joint Council for Qualifications (JCQ) in August.
The figures, for England, Wales and Northern Ireland showed that there were 157,699 entries for French GCSE entries, down 6.2% on 2014 and down around 11% on 2013.
For German, there were 54,037 entries, down 9.8% on 2014 and down around 14% on the year before, while there were 90,782 Spanish GCSE entries this summer, down 2.4% on last year and down 0.6% on 2013.
In October the Headmasters' and Headmistresses' Conference (HMC) and the Independent Schools Modern Languages Association (ISMLA) warned German could disappear from schools amid a "crisis in modern foreign languages".
A spokesman for Ofqual, which regulates exams, said: "Last year's results in modern foreign languages were very stable, with only small changes in the proportions achieving each grade compared to the previous year.
"We have looked into concerns that it is harder for students to achieve the highest grades in A-Level languages. We found this is because of the way the exams are designed, rather than the nature of the subject content, and we are keeping this under review."
A Department for Education spokeswoman said: "As global communication becomes easier, we know that employers increasingly prize the ability to speak a foreign language. That's why we made languages a compulsory part of the primary curriculum and since 2014, we have seen an increase in the take up of language A levels.
"By introducing the Ebacc, we have stopped the decline in modern foreign languages seen in the last decade, where 200,000 fewer GCSE students studied a modern language in 2010 than in 2002. Last year's results showed 20% more pupils are taking languages at GCSE than in 2010 while A level entries in modern languages have increased by nearly 4% since 2014."