The pressure on the curriculum, which makes it harder to offer students two languages at A-level, and the growing popularity of combined honours degrees or courses such as European or Latin American studies, which have less language teaching than a conventional degree, are just two reasons. At a time when many graduates are rejecting teaching as a poorly paid, low-status profession, languages seem especially at risk.
Without a good supply of language graduates, postgraduate education (PGCE) courses cannot fill their places. This leaves schools with neither the numbers nor the quality of teachers they need to offer the full range of modern languages and, in turn, means fewer young people go on to read the subject at university. Those that do may need extra help to bring their skills up to scratch.
"There is a direct correlation between the quality of teachers and the success rate of pupils learning a language," says Professor David Head, the head of modern languages at the University of Northumbria. "Because there have been problems recruiting, the quality has not been as good. It is not just that teaching has an image problem."
Other academics agree. "The shortage [in teacher training applications] is mirrored by the downturn in students taking modern languages at A- level and as a first degree," says Jean McKay, the dean of the school of education at the University of Wolverhampton. "As long as the subject remains in the curriculum as a mandatory subject, there has to be a supply of teachers."
Students who do go on to teach languages say that it can be a rewarding career - although it is not an easy option. Language teachers find that boys, especially, are hard to motivate. Kim Brown, a lecturer in education at the University of East Anglia, remarks: "The curriculum demands that teaching is in the language, which some children find very difficult. There is also a school of thought, especially for children who are struggling, that languages are an extra."
The best teachers are also good linguists. This is why university education departments have reservations about accepting students who studied languages alongside another subject. Their own knowledge of the language may simply not be enough.
"The nature of language degrees has changed a lot," says Kim Brown. "I did pure French for my degree, for four years. Now, you can get a degree in European Studies of which just 30 per cent may be French. You are getting people whose language proficiency is not enough to teach."
The language content of a PGCE course can go some way to making up shortfalls, and more universities are looking at introducing two-year PGCE courses, which are already common in the other key shortage areas, maths and science. Finance, though, is a problem, especially as most language graduates have already studied for an extra year.
The gap is being filled, to some extent, by native speakers from Europe who are keen to spend part of their careers in the UK. And some graduates are looking again at teaching, often because their jobs fail to live up to their promises of travel and using languages.
Angelique Parmentier, 26, decided to train as a teacher after working in sales for a well known food company. She now teaches French and German at Sutton Grammar School for Boys, in Surrey. She was unhappy in her job and started to think about other options. She had taught English one summer in Brussels and enjoyed the experience. "I had always been told that teaching offered very low salaries. I worked in sales, and earned a lot of money but didn't have a lot of job satisfaction."
She enrolled on the modern languages PGCE at King's College, London, and spent part of her course as an Erasmus exchange student at Linz, in Austria. "My PGCE year told me that teaching was what I wanted to do," she recalls.
Ruth Taylor, 25, studied with Angelique at King's and now teaches Spanish and French at Welling School. After graduating, she visited Colombia and taught English there, which she followed with a Tefl course. Ruth then spent two years teaching English in Barcelona, returning to the UK to teach languages because of Tefl's relatively limited career structure.
"Teaching languages is hard work, but you do have flexibility," she says. "You can reach kids at different levels. You can also be creative: you can speak, make them write or role-play."
Kim Brown adds: "Seeing pupils making progress and giving them opportunities to use the language are some of the rewards. There are also opportunities to challenge stereotypes, for example thinking about French-speaking countries around the world. Paris is a very international city. A lot of good language teachers would see that as one of the rewards of their job."
For language teachers, there is the added attraction of working with a community of like-minded people. "You are a recognised professional and part of a network of language teachers," says Professor Head.
"It is another life. You do get the opportunity to travel on school visits and exchanges. It broadens your network in Europe and offers another dimension to teaching that few other subjects do," he says.