I'm fluent in French and Russian - by which I mean that I don't have any trouble reading novels and can easily converse in either without making grammatical errors or feeling uncomfortable - and have been learning them for 2 and 3 years respectively.
Yet whenever I speak either with a native speaker (which, I should add is a rather rare occurrence) I am told that I speak like a foreigner, i.e. I don't use the right slang, etc.
Now it's hardly surprising, but something I feel rather uncomfortable about.
So, given that conversing with native speakers is a rather rare luxury for me, what can I do to make myself sound less 'foreigner-y'?