As discussed in this thread

https://developer.jboss.org/message/985930

my i18n properties have not been resolved on WildFly 14.0.1.Final - it was working fine through WildFly 10-13, however. I could solve the issue by renaming my properties file from messages.properties to messages_en.properties. Since this solved the issue, I suspect that WildFly 14 does not accept filenames without locale anymore. Since I'm not sure if this is by design, I'm posting this as a bug report here.