A Japan-only Professor Layton game is in the process of being translated.
Professor Layton and the Mansion of the Deathly Mirror was released for Japanese mobile phones in 2008, and is set between the events of Diabolical Box and Unwound Future.
The story involves Professor Layton and his apprentice Luke Triton receiving an invitation from mystery novelist Drebin Murdoch. Murdoch unveils a mirror that can speak with the dead, thus setting events into motion.
The first chapter of the game has now been translated into English by @Lilli208969, @NordicDestroyer and @frigamarrymepls.
In 2009, the game was re-released through the ROID mobile service under the name Professor Layton and the Mansion of the Deathly Mirror -Remix-, which featured all-new puzzles to solve.