To be clear, there was never a demo for part 2. The source of the confusion is that, looking at the GT page, there is a "demo" listed. But this is not actually a demo, it's one of the translations (and only the translation files). I experimented for a while with using the "demo" feature on Itch to distribute translations, as I wanted to be sure people could access them for free, but eventually stopped, for a simple reason: If someone needs to download the translations, they probably own a copy of the game already, and thus should be able to access translation files listed under the "paid" section without issue. But no, there's never been a GT demo, and there PROBABLY won't be for chapter 3 either. Visibility is limited on paid adult content on Itch now due to censorship, so I may eventually put SOME little thing out for free associated with 3 to raise awareness that it exists, but we'll see.
As for a German translation, all translations are fan-done, so a translation will happen when someone decides to do it. The required files are all there, nothing is encrypted in the release. Alternatively, RPGMaker MV can be fairly easily "hooked", using one program to capture text as it streams out, and another to translate that on the fly. It's not perfect, but it's certainly serviceable; machine translation has improved a LOT in the past decade.