Following up on this old bug report: Unreal 4.2x does support user folders with non-alpha-numeric characters. Confirmed on UE 4.27. This was broken again in the 5.x series due to mishandling the output log path (into User data). The bug report was closed and worked as designed - which seems to misunderstand the issue.
Within the project, there should not be unusual paths or file names. However, this item relates solely to the built environment itself, where Unreal is installed, and there is no technical or design reason for the limitation, it’s simply an error within the build scripts.