Dr Dan Tierney, a reader in languages at Strathclyde University, said the plan was welcome, but lacked coherency.
The warning is contained in a submission to the Scottish Parliament's European and External Relations Committee, which is looking at the issue.
In 2011, the Scottish Government announced ambitious plans to teach all primary pupils at least two modern languages. It came after a decline in the number of pupils taking modern language Higher exams that year, with figures showing a 4% drop in those sitting French, German and Italian, and only Spanish showing an increase.
Mr Tierney said: "It is unclear what we are trying to achieve here."