When we save config "DEFAULT BASE URL" in settings module this work for multilanguage with a path prefix, but if the used domain for language that the problem because for other language have one Base URL.
I think should give up base URL or leave it blank. Or move the base URL configuration to the form of a specific sitemapxml in list sitemaps (/admin/config/search/xmlsitemap).
Needs review
1.0
xmlsitemap.module
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I applied this but still have the same issue of the wrong URL on the sitemap based on the URL I ran to regenerate it.
Could you explain how this is working by language based on domain?
I tried passing the URI of each on using drush or regenerating via Rebuild tab, no success.