I don't know if this is the answer, because I have not used @Pattern, but in the docs, it says that the message field of the @Pattern is not a text, but a key into the messages file. Look here:
http://docs.oracle.com/javaee/6/api/javax/validation/constraints/Pattern.html#message()
By default message="{javax.validation.constraints.Pattern.message}" which looks like a valid key in ValidationMessages.properties file. I suppose you only have to specify a custom key and use it.