I’m using Discourse in French. Trial Business. Accented characters are common in French, surprised to see that the category name is not “prettified” (ie, strip the accents) for the slug and generates an error? Assuming this is a bug and not a feature…
「いいね！」 2
Hey there 
You should be able to set your category name with accented characters.
The category slug is something specific to the URL, so for example http://meta.discourse.org/c/bac-a-sable. I would recommend to just leave out the slug as it’s optional and will be generated based on the name. 
That was my assumption and exactly what I did — and got the error :-/
「いいね！」 1
Your screenshot shows that you entered non-ASCII characters as a slug.
If you leave that empty, everything should work as expected.
Is “Identifiant de la catégorie” a confusing translation for “slug”? If so, we should change that.
「いいね！」 1
Heavens 
My poor brain 
clearly encountered a bug… very sorry for the bother!
「いいね！」 2
No worries. Happens to all of us. 
「いいね！」 2