So can you actually play two different decks or you are forced to play one that works for both? (because the banlists are different)
Nekusar is not good in dedicated French EDH. That format is pretty cutthroat. I mean for a Vintage player that does not need to be a surprise but you can just die on t3. Happens and many decks are trying to kill fast even though more people play control with combo finish so they are slower.
In multiplayer if you want to win you can go all-in more or less but in French you'll be better positioned if you will use a control shell unless the tournament is going to be really big. For big tournaments (50+) I used to play all-in combos actually.

You should be looking for Time Twister effects (there's like 12+ of them), card draw and then some cards that helps kill your opponent (for example Fate Unraveler..or how it is called), underworld dreams can even abuse megrim effects if you won't take storm path