Thank you for your kind words; I'm glad you are enjoying Feather Wiki and finding it useful! :)
I don't have experience with Neocities directly, but if what I understand is correct, you should be able to just upload any HTML file to it, which means that you should be able to upload your Feather Wiki file directly to Neocities as well, just name it "index.html" instead of whatever the current file name is to have it show up by default at your Neocities address. :)
As for the names in the title, you should already be able to use whatever text you want in the title and headings of pages (and even in the page slug, excluding punctuation)! After testing with your example, I do see that the auto-generated link to the "Hörspiele/Hörbücher" heading is not correctly jumping down to the heading when clicking the wiki link from another page but removing the German characters does make it link correctly. It should be jumping to the correct heading regardless of what letters are used, so this is definitely not working as expected. I will be sure to address it in the next version!
Unfortunately while I can say that work on the next version is in progress, I cannot predict when the next version might be available. I'm hoping that I can make it available before the end of this year, but I can't promise anything unfortunately. I'll be sure to notify you in this thread when it is available so you can upgrade your current file and have the fix!