The remastered HD version of Professor Layton and the Diabolical Box (Japanese name: レイトン教授と悪魔の箱 EXHD for スマートフォン) now is available on western App Store ¹ (iOS) and Play Store ² (Android) at the price of $9.99 (tax included). As a western release, this client supports 3 languages in total including English, French and Spanish. It might also be noted that the game is playable in Japanese since Japanese client is due out on December 4th, 2018, for those who care can download it here ³ (iOS) or here ⁴ (Android) for ¥1,200 (tax included).
1) The currencies mentioned in this post are US Dollar and Japanese Yen, however these may vary based on country/region, hence there are some cases where currency exchange fee charge are required
2) Both App Store and Play Store do have region restriction, so the game is only visible for those who search it via an account had the location set to a corresponding region