Hello,

i'm sure how your Joomla website is running and is configured, but the problem looks like you have a plugin installed to make the website running on https and it replaces everything with https protocol.

Indeed the correct link in the sitemap XML document:
Expected: xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"

is replaced with the https version:
Found incorrect: xmlns="https://www.sitemaps.org/schemas/sitemap/0.9"

You need to identify the plugin that replaces everything with https and possible apply an exception for XML documents or the sitemap component to not alter the XML document.

I just answered you to the language pack question by email, you can answer me by email if needed.

Greetings,
John