"The French-speaking population of France during the French Revolution was estimated to be around 25 million people" (wrong, citing that same Statista graph that doesn't mention language use)
"It is difficult to accurately estimate the French-speaking population of France during the French Revolution, as there was no official census taken at the time." (honestly the most accurate answer yet, but citing that same Statista graph)
"It is impossible to accurately estimate the French-speaking population of France during the French Revolution, as there is no reliable data available. However, it is estimated that around 80% of the population spoke French in 1800." (first sentence is correct, second is wrong, citing that same Statista graph)
"At the time of the French Revolution, less than half of France's population could speak French. This was due to a combination of factors, including the fact that French was an extremely popular language with the elite and higher classes, as it was adopted by nearly all European courts and it even reached the other side of the Atlantic." (cites a babbel.com article; I think the first sentence is the first time the answer approaches both accuracy and consistency with both the question and source, largely by plagiarizing part of the source. It still omits useful context about the lack of literacy/fluency that's in the same sentence lifted from the source. Then it goes back off the deep end with the second sentence, which the source uses to emphasize how broadly French was spoken, and not as a reason why so few people in revolutionary France spoke French.)