How about - gently - taking a known set of English pedals and seeing if they'll fit the Stronglights? If they don't go on at all, fine, the cranks are French threaded. As far as these Lyotard pedals go, I would suspect the L and R indicate 9/16/BSC/ISO threads, because the comparable Lyotards on my outrageously French Liberia are marked D and G. You can gently thread these Lyotards into a known BSC crank and see if they feel loose nor not.

FWIW, the only Stronglight 93s I've owned that were French-threaded were on Peugeot PX-10s; all the others had English threads either because (a) someone decided bikes sold in the Anglosphere markets should have 9/16 threads or (b) someone ran some 9/16 taps through to convert them.