One in three secondary schools has cut the weekly lesson time for languages in key stage 3 - the only time when language learning is statutory - according to a new survey.
The annual Language Trends survey also shows that the number of pupils entered for a language GCSE has dropped again from 44 per cent in 2009 to 43 per cent last year.
The decline is almost entirely in state schools - 80 per cent have made languages optional compared with 11 per cent of independent schools.
The survey did not establish the extent to which weekly lesson time has been cut - only that the overall level has fallen.
The survey of 711 state and independent schools was carried out by Cilt, the national training centre for languages, the Association for Language Learning (ALL) and the Independent Schools' Modern Language Association.
Linda Parker, director of ALL, said: "The key stage 3 figures are really startling. If we are now looking towards a future which might see a revival in languages then we really need to consider how we are going to do that against a background of this continued trend of time being taken away from language learning in lower secondary."
Kathryn Board, chief executive of Cilt, said that current curriculum review and the introduction of the English Baccalaureate, which requires a language GCSE alongside four other subjects, could help revive languages.
But she said there was concern that it could undermine the alternative accreditations used by 45 per cent of schools.
Ms Board said: "This report sets out the gap to be closed if we are to rebuild provision for languages in schools where the subject has been pushed to the margins in recent years."
Languages were made optional at age 14 in 2004, but education secretary Michael Gove has said that the current curriculum review paves the way for them to be made statutory again.