Dummied Out: All of the four first games have 52 Wi-Fi puzzles (one a week for a full year) in the Japanese version. The English releases, on the other hand, have around 32. Finally averted as of Miracle Mask, where the number of Wi-Fi puzzles got bumped up to 365 (released daily) for all regions.
Fake Brit: Most of the voice actors in the English-language release of the games put on fake British accents. Actual British-English test players of the game reportedly hated Lani Minella's mockney accent for Luke so much that the British edition completely redubs Luke's lines with English-born Maria Darling. Christopher Robin Miller, however, put on an accent for the Professor so convincing that many players think he is British.
Series Hiatus: After the release of Azran Legacy in 2013, the series did not see any new title released until Layton's Mystery Journey: Katrielle and the Millionaires' Conspiracy in 2017, and the next main entry in the series wasn't so much as hinted at until Professor Layton and the New World of Steam was announced in early 2023.
Unspecified Role Credit: While the games' credits do list the names of the voice actors, they don't tend to specify who they voiced outside of the original Japanese releases. There are some confirmed English roles, such as Christopher Robin Miller as the professor, Chelmey, and Don Paolo; Lani Minella as Lukenote replaced by Maria Darling in the UK version and Flora; Yuri Lowenthall as Future Luke and Randall; and so on, but good luck figuring out who voiced characters like Badger and Sheffield. Mystery Journey also had a variation of this trope that actually listed the exact voice actors for each main character, but put all of the others under "Supporting Cast".
Professor Layton and the Diabolical Box was first intended to take place in a tropical island where Layton must use his puzzle skills to survive, but the designers realized that such a situation wouldn't be very gentleman-like. However, he does go to a tropical island in Professor Layton and the Eternal Diva.
According to the art book, Descole was originally supposed to have a large Plague Doctor-esque bird mask. This design was later reused for the Black Raven.
