What Amazon will stream is an English dub spanning 26 episodes, narrated by everyone's favorite FBI agent, Gillian Anderson. She has a bit of history with Ghibli as she did the voice for Moro in the Princess Mononoke dub, which was handled by Disney. So, the chances of this being a solid version with western voice-overs are probably pretty high. But, again, it's important to note that this isn't a full-on Amazon Original. With Studio Ghibli on hiatus, this might be the last bit of the team's work, so make the most of it.
For those with little kids (and who aren't just young at heart themselves), Amazon has also ordered Little Big Awesome which features flying sea turtles and "a jelly giant." That hails from Ben Gruber of Spongebob Squarepants and Super Jail fame, and is being animated by the house of Metalocalypse, Titmouse Inc. It probably won't be brutal, but we can always hope for a William Murderface Easter egg, can't we?