Yes, the linked articles are in French. I have been looking around for good background material on the Gauls, and much of it is in French (naturally, since Gaul is approximately covered by modern France, Switzerland, Belgium Holland, and western edges of Germany). But some here on AW speak French natively and others such as myself can read it, so ....

The French site L'arbre celtique has an interesting and scholarly article Rites et classe sacerdotale : inventaire des textes anciens by the well known French archaeologist and author Patrice Lajoye. The same site also has a companion article Le druidisme antique by an unspecified author.