The only French word with a "x" I could find that has a German equivalent is "Aix-la-Chapelle" with German equivalent = "Aachen". The French UK dictionary said flatly that "x" in French is pronounced "ks", no exceptions noted.

But I could not find the pronunciation of "Aix", but looking at the German antecedent, the "x" may have been pronounced in the the beginning. This added after AS corrected me.