Labor is not fungible. A janitor can't take a week training course and become a surgeon.

So France is suffering from an influx of immigrant surgeons?

Its not appropriate to answer here in a few lines since France suffers from many issues related to education, a social net that removes incentive to do some kind of work, quotas in certain activities and immigration thats completely uncontrolled. It is a complex set of problems yet the conclusion is not that France needs to import more workers. Its rather an issue on how existing resources are allocated.