Try the following:
Edit JBOSS_HOME//server/(default)/deploy/jboss-web.deployer/server.xml and edit the following line (I guess UTF-8 should be Ok, but I think you'll have to try with other values as well):
<Connector port="8080" URIEncoding="UTF-8">
Edit eithr JBOSS_HOME/bin/run.bat or JBOSS_HOME/bin/run.sh depending on the OS you're using. Set the -Dfile.encoding option accordingly (again, try first UTF-8):
JAVA_OPTS=JAVA_OPTS -Dfile.encoding=utf-8