Okay I tried again. It works indeed without changing xorg.conf:
0) Keyboard properties / Layout
1) Add "Germany Dead grave acute"
2) Remove "Eliminate dead keys"
The UI isn't very logical, though. It shouldn't be possible to enable both options at the same time. There
doesn't appear to be an option for "dead circonflexe" - drôle (cannot be typed without composite key).
Okay I tried again. It works indeed without changing xorg.conf:
0) Keyboard properties / Layout
1) Add "Germany Dead grave acute"
2) Remove "Eliminate dead keys"
The UI isn't very logical, though. It shouldn't be possible to enable both options at the same time. There
doesn't appear to be an option for "dead circonflexe" - drôle (cannot be typed without composite key).