I have installed jEdit 5.0 from Ubuntu distribution. My locale is Russian.
When installing XML plugin with Plugin Manager I get FileNotFound exception in activity log and plugin is not installed. It happens because I'm installing plugin with source and unpacker in Plugin Manager cannot handle non-ASCII character in folder name
When installing plugin manually there is no such problem, since "XML-2.8.5.zip" contents is unpacked by standard Ubuntu archive manager.