Hi Jeff, sorry for stealing your time. I found the error. It was in the FTP client file zilla. Namely, in the server manager the charset was set to auto detect. And i have now set it to force UTF-8.
Now I can reach the page.
I came up with this because after transferring folders with umlauts, I could see them on the server but I couldn't delete them. I had to delete them through the console via the raspian. Now I know why.
At that time I thought, the server can't handle umlauts and I accepted that. In my website programming I have always avoided folders with umlauts. Until jAlbum created them automatically and there it was again, the problem.
Thank you anyway for helping me with my problem.
Maybe we come together again with the next problem.
Greetings Mario M. (Germany/Hessen home of "Ahle Wurscht")