I found that it was much more elegant to get rid of the ValidationMessages_XX.properties files. Just all the localized configuration in one file that supports UTF-8!
The answer is to set the ValidationMessageSource of your validator with your resourceBundle. For example:
<bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource"
p:defaultEncoding="UTF-8"
p:basenames ="classpath:messages"/>
<!-- JSR-303 validation-->
<bean id ="validator" class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"
p:validationMessageSource-ref="messageSource"/>
All merit must be attributed to this blog post. Not being able to read thouse characters was annoying. No more: message=\u042D\u0442\u043E \u043F\u043E\u043B\u0435 \u043D\u0435 \u043C