For me, the templates plugin has stopped working well after update from jEdit 5.1 to 5.3. I was hoping that an update to jEdit 5.4.0 and templates 5.0.0 would fix the problem, but unfortunately it didn't:
Whenever I try to insert a template this fails with an error dialog: "An Error occurred while attempting to process a template. Refer to the Activity Log ..." (Templates plugin 4.1.2 didn't show this message, it failed silently). The Activity.log then contains a "java.lang.NoClassDefFoundError: org/apache/commons/lang/StringUtils".
The error occurs in these environments (see attachments):