Hi Mike.
Access is relatively easy once you know where
There are maps available of the GSN (Great Southern Network) which are very accurate and make navigation easy.
There is no need to speak french at all except in the bar ("deux pression s'il vous pla?t")
It is actually illegal to explore the catacombes, however nobody seems to care, there are always quite a lot of people down there at weekends with parties and stuff happening in various rooms.
You do run the risk of being caught and fined but this has only happened on one occasion to UK cavers that I am aware of. They managed to escaped a fine by pretending to not understanding french, then promptly went straight back underground
Kit is just old clothes and overalls, phone me up if you are serious and I will give you lots more info.