Please file a bug report in JIRA. Include clear reproduction steps.
Hibernate validator 3.0.0 GA uses Locale.getDefault() to determine the locale of messages, apparantly this problem is resolved in 3.1.0 CR2.
you can fix this problem temporarily by changing the default locale in your action.
It looks like I'm falling in the same trap. I'm currently using JBoss 4.2.3.GA and Seam 2.1.1.CR2, with an ear packaged project that does not include (in the ear) any hibernate lib (as I suppose they are provided by JBoss). With this configuration, it looks like that when changing the seam locale the hibernate validator messages are not affected.
After reading the previous message I checked which version of Hibernate Validator is provided by default with JBoss 4.2.3 and, to my surprise, I wasn't able to find the library (where is it btw?).
In any case, I noticed that the other hibernate lib are a little old so I swapped them out and included what I believe is the latest version (that is Validator 3.1.0 GA, Core 3.3.0 SP1, Annotations 3.4.0 GA and Entity Manager 3.4.0 GA, plus other dependencies). Unfortunately the result was the same: once the validation message has been shown in one locale, changing the locale through seam doesn't affect the validation messages already loaded by hibernate and at the next validation the message in the old locale is shown.
Any idea why? Suggestion to solve the problem?
PS: btw, I've also found and old, solved, JIRA issue that seems related JBSEAM-1880 and marked as solved, but the problem seems to be still there.