English Translation
Joan is as charming as her sister.
The translation for this sentence is “Joan is as charming as her sister”. The sentence uses the masculine form of charmant which I thought might be an error, as I was expecting charmante.
Well, it turns out that Joan is one of those names that is ambiguous across languages like Andrea, Nicola etc. as demonstrated by looking at the French Wikipedia page -
So, while the sentence/translation is mismatched (since the English considers Joan to be a feminine name), there is nothing wrong with the sentence itself.