I know that it’s possible to port a WordPress site, but in terms of an existing site? It’s not impossible, but might be tricky, depending on the number of pages you have…
I’m currently in the process of porting an existing Wix website to Publii, but it’s going to take a while.
In terms of other languages: In Publii, click on the three vertical dots at the top-right, and click on “Languages”. Click on “Get more languages”. You’ll be taken to this link: https://github.com/GetPublii/Publii-ui-locales.
It looks like German is “In Development”. You can add to the discussion here: https://github.com/GetPublii/Publii-ui-locales/pull/4