Modern languages should be compulsory for the vast majority of 14 to 16-year-olds under the proposed diploma system, says a new report from the Nuffield Foundation.
The paper, written by Kathy Wicksteed of the Specialist Schools Trust, after discussions with policymakers and academics, says pupils are unlikely to choose languages if they are optional because they are seen as "difficult".
The curriculum for 14 to 19-year-olds is under review. A diploma system has been proposed by Mike Tomlinson, the former chief inspector, but not yet adopted by the Government.
Mr Tomlinson's interim report on the 14-19 curriculum says that maths, communication and ICT should be compulsory for all pupils, but other subjects would be optional. Post-16 specialist diplomas would include courses for pupils wanting to follow a particular employment or academic route, such as leisure, travel and tourism or social sciences.
Ms Wicksteed, a curriculum team leader, said: "If pupils' needs rather than preferences are to be met, some level of compulsion will be essential.
"In preparing students for the realities of the workplace, it is hard to justify tourism or business courses that do not require any foreign language competence."
Languages will become optional for 14-year-olds from this September. The Government has said that instead of compelling 14-year-olds to do languages, it wants pupils to become enthused in primary schools. All primaries will be expected to offer language lessons to junior-aged children by 2010, but they will be free to choose how they do this.
An assessment system, called the language ladder, is being developed, which grades the abilities of pupils of different ages following different courses. The scheme will allow schools and colleges to devise their own courses, but end up with a single nationally-recognised grade.
The levels of the ladder are described in "can do" statements - listening level 2, for example means: "I can understand a range of familiar spoken phrases". It will be used alongside public exams such as GCSEs.
The contract to develop the 14-rung language ladder has been awarded to the University of Cambridge Local Examinations Syndicate and is worth around pound;7 million.
The system will have both external and internal exams. Teachers will be able to train to become internal assessors, using materials provided by the scheme. These assessments will be available at all 14 stages.
External exams will only be available at six points, roughly equivalent to the level expected at primary school, foundation GCSE, higher GCSE and A-levels with the highest two rungs for university courses.
To offer the external exams, schools will have to pay to register as examination centres - something primaries may be reluctant to do.
Monica Galt, head of King's Road primary, Manchester, where French and Spanish are taught, said: "People will not pay to test pupils, so what is the point of it? It will become rather selective."
Schools are wanted to pilot the language ladder: contact 01223 553998