Ignorance of the linguistic reality
I know the writer/s are trying to make Queen Isabella seem like a really foreign and therefore alien character by upping her Frenchness, but it doesn't make cultural sense for this era as the entire monarchy and most of the nobility were Norman French speakers. Many of the royals could speak no English at all.
So by having Edward III seem very English in comparison to his mother is culturally silly as the entire Plantagenet dynasty were proud native French speakers who had disdain for the English peasantry. English did not become the royal language until a decree by Henry V in 1410.