When using the Sitemap.xml file functionality in the SXA module for multi-language sites, the <loc> node in the created XML file is the same for all language versions. This leads to the fact that a URL getting generated in the sitemap does not have any language code embedded when trying to access the sitemap in the browser. Each URL is repeated as many times as the number of language versions that you have but without language code.
This issue affects SXA 1.6.0 and later versions. It was fixed in SXA 9.3.0.
To resolve the issue, download and install the patch or hotfix compatible with the affected product version:
Be aware that the hotfixes were built for specific Sitecore XP versions, and must not be installed on other Sitecore XP versions or in combination with other hotfixes. In case any other hotfixes have already been installed on a certain Sitecore XP instance, send a request for a compatibility check to Sitecore Support.
Note that ZIP file contents need to be extracted to locate installation instructions and related files inside it. The hotfixes must be installed on a CM instance and then synced with other instances using regular development practices.