Hi, I'm a Japanese WildFly user and it works fine at most of situations with Japanese characters so I think I can help you, but not sure what problem are you facing. could you write more information here about the issue?
A typical problem with Japanese characters issue I know is corruption of POST parameter. it will be solved with placing /WEB-INF/jboss-web.xml which contains following content:
<?xml version="1.0" encoding="UTF-8"?>
<jboss-web version="8.0" xmlns="http://www.jboss.com/xml/ns/javaee"