CustomLocaleResolver.groovy

class CustomLocaleResolver extends SessionLocaleResolver {
    def springSecurityService = Holders.grailsApplication.mainContext.getBean('springSecurityService')

    Locale resolveLocale(HttpServletRequest request) {
        //getting locale from session
        Locale locale = (Locale) WebUtils.getSessionAttribute(request, LOCALE_SESSION_ATTRIBUTE_NAME)
        if (!locale) {
            if (springSecurityService.isLoggedIn()) {
                def user = springSecurityService.getCurrentUser() as User
                locale = user.locale ?: determineDefaultLocale(request)
                //put user's locale to session
                setLocale(request, null, locale)
            } else {
                locale = determineDefaultLocale(request)
            }
        }
        return locale
    }
}