I have a brand new server and installed:
Ubuntu 16.04
Oracle Java 8
xwiki-tomcat8-mysql (DEB package from XWiki repo)
This installed XWiki 9.9. Before doing anything else, I inserted a code macro with nothing ("") in the language field and get the following render error:
Failed to execute the [code] macro. Cause: [Failed to find engine for Python script language]. Click on this message for details.
Changing the language type to “none” resolves the issue!?!