Awesome, Dear Boy: Christian Bale said he'd play any role in the English dub after he saw Spirited Away and loved it. He didn't expect to land the title role.
Crispin Freeman lobbied hard to get a role (any role) in the movie. He was originally up for the very small role of the soldier who hits on Sophie. He was eventually cast in the small but much more significant role of Mr. Turniphead aka the Prince.
Crossdressing Voices: The Witch of the Waste, but only in the Japanese version, where she was voiced by Akihiro Miwa, a Japanese actor and drag queen.
Fake American: Christian Bale uses an American accent in the dub of the film. Ironically, Howl's eventually revealed backstory in the book reveals him to be a Welshman like Bale himself. Thus, he could've used his natural accent to play him and it would've fit.
Fake Brit: Jena Malone uses an English accent in the dub to play Lettie - to better match with Emily Mortimer and Jean Simmons voicing her sister. Funnily enough, she'd do the same in Pride & Prejudice (2005) around the same time.
Pop-Culture Urban Legends: A fan rumor is that Hayao Miyazaki was inspired to make the film after visiting the Strasbourg Christmas Market.
In Hellboy (2019), Baba Yaga's walking home resembles the titular castle, in contrast to the simple cabin she has in the Hellboy comics and the folklore.
Anna from The State of Grace has a huge crush on Howl. When she describes a boy as "cuter than Howl," Grace knows she's serious about him.
Shout-Out: A really subtle one was added by the Swedish translator. When Howl shows Sophie his secret garden and talks about his wizard uncle, the dub has him refer to him as "my uncle, the wizard". That is a nod to The Magician's Nephew which is called "my uncle, the wizard" in Swedishnote Swedish differentiates maternal and paternal uncles. Howl specifically uses the paternal word as opposed to the maternal used for The Magicians Nephew which does make the nod a bit subtler.
Stunt Casting: Lauren Bacall was cast as the Witch of the Waste in the English dub partly because she was one of Hayao Miyazaki's favorite actresses.
Throw It In!: The distinctive growl that Christian Bale uses as Batman can be heard in the English version. This is because he was preparing for Batman Begins at the time.
What Could Have Been: Director Mamoru Hosoda was originally brought on to helm the project when the film was announced, but he would quit the project and Studio Ghibli in 2002 due to being dissatisfied with Ghibli's strict Executive Meddling and working conditions, as well as incompatible Creative Differences over the style and tone of the film, with Ghibli wanting Hosoda to replicate Hayao Miyazaki's worknote Miyazaki was "retired" at the time, while Hosoda wanted to make the film in his own style.
