Re your comment on my comment on your proposed translation, yes, antitrust violations (the US equivalent) can carry criminal and/or civil penalties. Broadly speaking you can tell which sort it is by who's on the other side from the defendant: federal prosecutors? Criminal. Another company in the industry? Civil.
But the question here is whether violating the
French statute at issue (art. L.420-1 of the Commerce Code) carries criminal, civil, or both sorts of penalties.
If this FR statute can't carry criminal penalties, then you can't properly use the word "guilty" in your EN translation. Here, the complainant is another company in the industry, so we're almost certainly looking at a civil issue rather than a criminal one ("almost" because I don't have time to look up whether criminal penalties can be part of this sort of civil case in France).
If we don't know or don't have time to research the penalties, then
"culpable" could work because it means at fault or blameworthy--it leans criminal ("culpable homicide" etc.) but is not exclusively criminal:
https://thelawdictionary.org/culpable/