i've never used crowdin, but i'm willing to look the french translation file over. If you'd rather send the resx, and that I work on that, that's ok too. Username is botmtl.
If you want to make the changes yourself, this is good (changed adaptations for ajustements because that's the text used in the menu). Does the english version mentions that paintdotnet allows editing of "pictures and images" or simply images?
"ApplicationName"="PaintDotNet""ApplicationDescription"="PaintDotNet permet de créer et d'éditer des images et photos à l'aide d'un large éventail d'outils, d'ajustements et d'effets."