Both my eighties Pugs used perfectly ordinary 1" standard threaded headsets. If you're in any doubt the best bet is always to take the bike, or at least the original part to your LBS. If you don't have vernier calipers and a thread gauge they probably will have.
Yes older French bikes used odd threads, but then so did Raleigh. Generally speaking the older the bike of any nationality the more likely you are to find uncommon sizes and threads.
