Hi, I'm not able to update the game right now but you can add the German localization by copying one file from the Steam version to the itch.io version (you get a steam key if you buy the game here)
The file is C:\Program Files (x86)\Steam\steamapps\common\Pepper's Puzzles\assets\localization\de.json
Just copy it to the same folder of the itch version and the German option should appear when you next launch the game.