Hi! Thank you for your answer & questions...
Can you type letters such as ä in your Moodle text editor? -> yes -> letters are correct when typing & afterwards
if you copy/paste the text into the editor? -> same answer - everything is ok
Content of zipped file looks ok when extracting it to my pc (windows) and all individual files looks correct at browser.
I've uploaded file to create www-page inside of Moodle. First upload zip - then extract it - then went to created folder and choose index.html as a main page.
For me this looks similar if I upload multiple users from csv-file and not choosing UTF-8 coding. But there is no place to choose coding when uploading www-page.
I just also tested when uploading single www-page (I put that page as a attachment here) -> so it is doing exactly same. If you have time to check do you see that page correctly in your browser and what happens when you're trying to upload it to your moodle... Is that possible?