Atlantis: The Lost Empire
While I really enjoyed this movie and the fact that the protagonist is a linguist (because I love languages), the linguistics in the movie are terrible.
First off, while Milo is running through his speech in the intro, the runes he is working with seem to be a 1-to-1 cypher for English (to the extent that a single mis-transliterated rune changes the meaning from coast of Ireland to coast of Iceland.
Then there's Atlantean: in no way does being the forerunner of all modern human speech (which is essentially what Milo calls it, on first encountering the Atlanteans) make it possible to understand all modern human speech. Think of it this way: The romance languages (French, Italian, Spanish, Portuguese, Romanian, etc.) are descended from a common ancestor (Latin), but are not mutually intelligible.
Now, if you brought a Latin-speaking Roman forward in time, he would not be able to understand what was being said by any speaker of the Romance languages, because they have mutated over time to be very different from their common ancestor. Now I'm not saying the Roman wouldn't pick up some words that sound familiar, but even I did that when listening to the Swedish dialogue of The Girl with the Dragon Tattoo (which, by the way, had the best representation of computers I have ever seen in a movie). And anyway, even if being "descended from a root dialect" (aren't all languages descended from root dialects?) makes the descendant tongues intelligible to you, wouldn't that work the other way as well?
I can only assume it's actually the Heart of Atlantis that's helping the Atlanteans speak to the outsiders.