Since seam uses hibernate validator internally when using the tags s:validate and s:validateAll, I think it should update the locale used for hibernate validator messages when one invokes localeSelector.select
Obviously, it doesn't since the hibernate validator error messages are in the language specified in the browser preference settings rather than the seam locale.
Issue added to JIRA
http://jira.jboss.com/jira/browse/JBSEAM-1880