I'm not sure if this is to be suggested here. But I'd say French site GUI is now somewhat ordinary. Look at sibling Stack Exchange sites, say, English, it feels more classic. Look at mathematics site, it's also more exciting.
Is there any plan to make this site's style, logo, icon, etc… more attractive?
All public beta sites have the same theme, which now indeed looks a lot like the Stack Exchange site.
Sites only get a custom theme once they graduate out of beta, so you just have to wait until that happens for French Language and Usage.
If you want to discuss the future theme (not sure if that's appropriate yet), I guess proposing something here is the right way to go.
The switch won't happen before the site has graduated, but you can have a look at design proposals that have already been suggested:
What should our logo and site design look like? Idées de conception visuelle du site
Please add your own ideas if you have any.
