indivisible spaces

Hello there !
I’m still discovering Scrivener, but I can already say that it is awesome !
I’m french, and I’ve got some custom stuff to set in order to have my project correctly tyopgraphied.

I’m especially looking for a way to show indivisible spaces.
Actually, it’s said that alt+spacebar will insert an indivisible space, but how can I be sure I did’nt make any error? In open office, for example, indivisible spaces display as thin gray bars, unlike normal spaces which are blanck.
I found “format/options/show invisible caracters”, but I don’t see any difference between normal and indivisible spaces.

Also, the french dictionnary is quite… incomplete. I saw many people have the same issue, and I should be able to replace usual dictionnary file by another one, but I would be glad to have à link toward a french dictionnary somewhere in the internets, cause I’m definitely not sure where to look for.

Thank you for helping !