Of course, with just a single tweet there isn't much additional information about the iOS release for the original Professor Layton game in the United States. Given that this will be a direct port of the game, it appears that Professor Layton and the Curious Village will not be one of Nintendo's mainline apps that are taking established characters and franchises and making them into mobile-friendly titles, like Super Mario Run and Animal Crossing: Pocket Camp.
Since the first game, the Professor Layton series has seen numerous sequels over the years, with the last game coming out in 2017. That game, Layton's Mystery Journey, was the first sequel in the series to debut on mobile [iOS Direct Link] alongside the release on Nintendo 3DS. Otherwise, the original Professor Layton games had yet to make it to the iOS App Store before now.