I think I get a workaround, following what I found here.
So… I tagged all the subfolders in Resource with a “Moderated” tag and set up a workflow as follows:
File system tag → is tagged with Moderated (invisible) → tag the file with to moderate.
And it works.
By the way, the translation in french of File system tag, which currently is Etiquette collaborative du fichier is just ununderstandable! 
Reverse translated it would be Collaborative file tag. Do you feel like it’s the same? Not at all!
Etiquette du système de fichier would be a literal translation, but even this is not as precise as the english version and Etiquette du file system or even Etiquette du fichier/dossier (file/folder tag) would even be more understandable.
Yes I know, I can contribute to the french translation, but I’m doing it here and there and I can’t be everywhere. Sorry.