After the purchase of France South LoMaps, the cartography was not available via the LocusMap normal menu.
Then,I founded the two files (*), and they were stored not in the "france" folder, but just above, in the "europe" folder...
Finally, all became OK after a cut and paste of the two files to the france folder...
(*) _france_south.osm.db (305 Mo) and _france_south.osm.map (1,14 Go)