Based on mutual intelligibility:
* Occitan is often considered the closest, especially in its southwestern dialects. Speakers of both languages can often understand a fair amount of each other.
* Spanish and Italian are also relatively close, with some shared vocabulary and grammatical structures.
Based on historical and linguistic relationships:
* Occitan again is closest, being part of the same Romance language family as French and sharing a common ancestor in Vulgar Latin.
* Spanish and Italian are also close relatives, all belonging to the Ibero-Romance branch.
* Portuguese is slightly further out, but still within the Ibero-Romance branch.
* Catalan is part of the Occitano-Romance branch, making it close to Occitan and thus to French.
Based on specific linguistic features:
* Occitan has a lot of similarities with French in terms of pronunciation and grammar.
* Spanish shares many cognates (words with a common origin) with French.
* Italian shares some grammatical features and a similar rhythm with French.
Therefore, depending on your criteria, the closest language to French could be:
* Occitan if you focus on mutual intelligibility and historical relationships.
* Spanish if you focus on shared vocabulary and grammatical structures.
* Italian if you focus on shared grammatical features and rhythm.
Ultimately, "closeness" is a subjective concept, and different people may have different opinions based on their personal experiences and perspectives.