I've never had any problems filtering in France and I've done a lot. In fact it always seems to be expected and French riders never hang around in queues of traffic. In fact they can be a big danger as they zoom up behind you... I ride to Beziers in the S of France every year from Calais - the Paris peripherique - Bourges - Millau. Last year I was filtering steadily through a queue of stationary cars on a long stretch of road heading South from Bourges when I noticed a blue light coming up on the hard shoulder. The cop drove alongside me and gave me in sign language and a very frowny face an order to pull in and stay in lane. I did and fortunately stayed that way for a few miles. He'd parked further up the road and gave me another frown but a thumbs up. I found out later that filtering through slow-moving or stationary traffic is actually illegal in France. You live and learn.