Take-up of traditional languages at GCSE level is falling
Four in five secondary school students across the EU ought to be learning two European languages by 2020, the European Commission has said.
Currently in UK secondary schools, pupils are not obliged to study any modern language past the age of 14.
The National Union of Teachers said there were not enough trained language teachers to deliver the EC's proposal.
The government's target for England is for at least half of secondary pupils to take a GCSE in one modern language.
The proportion of secondary schools able to offer two languages to GCSE level is relatively small - 45%.
Christine Blower, acting general secretary of the NUT, said of the EC's proposal: "This is an entirely laudable aim."
But she questioned where the trained teachers might come from to achieve it.
The document from the European Commission is part of a framework for co-operation in education and training.
It sets out how EU member states have been co-operating since 2000 to achieve certain benchmarks in education, including reducing to 10% the proportion of children who leave school prematurely.
The EC document says it will discuss with member states proposals for 10 new benchmarks to be achieved by 2020.
These include "to teach two foreign languages to at least 80% of children in lower secondary education".
Some European countries such as France divide secondary education into a lower and higher age group, with a lower school for 11 to 14-year-olds.
The EC also proposes reducing by 15% the proportion of children aged 15 with low attainment in maths, reading and science and ensure that 90% of children under four are receiving a pre-school education.
Exam entry figures show that languages traditionally studied in schools in England, Wales and Northern Ireland are declining in popularity at GCSE level.
In 2008 there were 201,940 GCSE entries for French, 3.6% of the total exam GCSE exam entries, down from 216,718 in 2007.
Christine Blower added: "You have to have regard to the background to the debate about learning a foreign language.
"Many children come to school already speaking a second language, which have value in terms of their identity, and this is an under-considered aspect of this debate."
She said central government policy on languages had been "all over the place over the last 10 years".
"Where schools were under pressure, they cut modern languages departments," she said.
"Where are we going to find these language teachers?
"The absolute worst thing would be to constrain teachers who aren't qualified to teach them."
The government's target is that all primary schoolchildren should have the opportunity to learn a language by 2010.
A spokesperson for the Department of Children, Schools and Families in England said they wanted between 50% and 90% of all secondary school pupils to gain a GCSE in one foreign language.
In its response to the communication, the minister for further education, Sion Simon, said the time was "ripe to consider objectives and working methods for 2010 - 2020".
The European Scrutiny Committee of the House of Commons described the proposals for new benchmarks as "ambitious".
The EC document will go on to be scrutinised by the European Council.