Hello and welcome frenchuser666!
To my mind there is no legal issue with YaCy use in France, especially for personnal use in peer-to-peer mode. Providing links to some illegal pages among other search results should not be an issue : it really is not the same as publishing an article which contains links to some illegal material you eventually endorse.
What's more, YaCy has a black listing feature that allow you to prevent storing links or indexing sites you really don't want to. The black lists can be shared and reused between YaCy users.
To my mind an eventually illegal use of YaCy would be to configure it as a search portal publicly available, whose unique purpose would be to provide links to illegal material you index, eventually with a custom main page mentionning the purpose of this portal.
Further readings that might interest you :
- Tim Berners-Lee (the Web "inventor") point of view (1997) about links and law : Links and Law: Myths
- a W3C (Web Standards organization) more recent paper (2013) about Publishing and Linking on the Web
helps clarifying the situation
- Lumen (a project collecting cases about online content), and their dedicated page about linking
PS : I also think the forum search is broken. Maybe @Orbiter can tell us more?