One thing I am familiar with is the European Convention on Human Rights which grants Freedom of speech in Article 10 and which is binding in France.

Edit: There is no state in the world where there exists some sort of "absolute freedom of speech".

Freedom of expression/freedom of speech is guaranteed in some way in all Western nations, the difference – as you correctly point out – is the degree to which other rights are also taken into account when applying the Right to freedom of speech. But that's an extremely important distinction and it cannot be said that France doesn't have Freedom of speech.