I love it but by the time I read it I had SOME knowledge of historical language change (thanks 4th year Spanish teacher making us read snippets of Don Quixote in the original). There is no way this remote fishing village would speak a dialect completely intelligible to the entire continent.

as i was reading these books 2 or 3 years ago, i think i justified it to myself with the idea that having dragons made it easier for them to keep their language uniform, so it drifted but didn't fragment, analogous to the internet

It's also in the story that their village has historically had limited contact. Very few folks travel away and stay for for any length. I can imagine a language that is shared as prestig and a subset is used for trade but not that everyday colloquial language wouldn't drift a lot.