Head teachers and language experts say it is harder to get good grades in modern languages than other GCSEs.
Language lessons are no longer compulsory after 14
They are calling for exam grading in modern languages to be brought into line with other key subjects.
The Association of School and College Leaders (ASCL) says the system is unfair and is putting pupils off studying modern languages.
England's exams watchdog, QCA, has rejected calls for a re-grading, saying such action could be harmful.
The Association of Language Learning (ALL) had suggested to a review of languages by Lord Dearing that there should be adjustments to the grading of GCSEs to redress what it said was the imbalance between languages and other subjects.
England's QCA, in a report, says there are counter-arguments and that instead the focus should be on improving teaching and raising pupils' performance.
It says: "The present examination system is not based on an aptitude-based conception of comparability and its adoption would create a major threat to public confidence in students' results.
"We have similar concerns about applying a new performance standard to languages but not to any other subjects, some of which might also want to claim special status.
"We do not have evidence that there have been significant changes to grade standards in GCSE languages in recent years. In conclusion, we do not therefore, recommend any adjustment to national grade standards in GCSE languages."
Earlier this week, it was announced that oral examinations were to be changed from one test at the end of a course to several assessments, because the existing orals system was believed not to be fair on students.
The Association of Language Learning (ALL) and the Independent Schools' Modern Languages Association (ISMLA) were disappointed by the QCA's verdict.
Helen Myers, president of ALL, said: "We are pleased that the QCA acknowledges that there is 'severe grading' in modern languages and so there is a definitive statement that pupils of similar prior attainment will on average gain a lower grade in languages than mathematics.
“Whatever QCA argues, there is an implicit and explicit assumption that a C in one subject is worth the same as a C in another.
"The report correctly states that a complete change to the grading system would not command public support.
"But this is no reason for not addressing the most glaring anomaly in GCSE grading, which is discouraging pupils from studying languages post 14 and leading to situation where the majority of pupils aged 14-16 have dropped modern languages."
Dr John Dunford, general secretary of ASCL said: "The main problem is that modern language GCSEs are graded more severely than other subjects and it is extremely disappointing that the QCA, while recognising the problem, does not intend to bring the grading of GCSE languages into line with mathematics, English and other similar subjects.
"The report clearly accepts that it is more difficult to get a good grade in a language GCSE. Students and their parents have known this for years and it is therefore no surprise that the number of students taking languages has plummeted since they were made optional.
"This is not an issue of 'dumbing-down' language GCSEs, it is levelling the playing field with other similar subjects so that languages appeal to a wider range of students."
A QCA spokesperson said: "QCA has found no evidence that the grading of GCSE language exams has become more severe in recent years.
"To lower standards based on a statistical comparison with other subjects would undermine the current basis of grading decisions.
"Grades must be based on the professional judgements of subject experts using the evidence of candidates' work. Instead, we should focus on improving learning in modern languages in order to gain students' commitment and raise performance."