Conforme xorg docs e archwiki :
You must specify as many variants as the number of specified layouts. If you want the default variant, specify an empty string as the variant (the comma must stay)
ou seja,
setxkbmap -layout "L1,L2, ... ,Ln" -variant "V1,V2, ... ,Vn"
No seu caso:
setxkbmap -layout "de,fr" -variant "nodeadkeys,basic"