Hibernate Validator: Violation Message Language

I have a test class where I am testing a domain model which is annotated with e.g. @NotNull

In my test class I am first getting the validator

private static Validator validator;

@BeforeClass
public static void setup() {
    validator = Validation.buildDefaultValidatorFactory().getValidator();
}

Later I have a JUnit Test where I am testing the domain model (lets say a Person)

Set<ConstraintViolation<Person>> violations = validator.validate( aPerson );

Lets say, I want to retrieve the first violation Message I do:

String violationMessage = violations.iterator().next().getMessage()

I haven’t set any custom violation message on the @NotNull annotation. So hibernate validator will pull the default message from the Resource Bundle which is in the hibernate-validator-jar. My path looks like this:

hibernate-validator-5.3.5.Final.jar
    - org
        - hibernate
            - validator
                ...
                ResourceBundle 'Validation Messages'

In this Resource Bundle there are quite a few languages supported (English, German, French, …)

Example

@NotNull violation message in German

javax.validation.constraints.NotNull.message     = darf nicht null sein

@NotNull violation message in English

javax.validation.constraints.NotNull.message     = may not be null

Question:

When I am testing, how can I enforce Hibernate Validator to choose a specific language for the violation message from the Resource Bundle? Right now, I am getting English violation messages. However, on another machine German.

Answer

Summary condensed from the reference docs:

By default, the JVM’s default locale (Locale#getDefault()) will be used when looking up messages in the bundle.

Without touching source code or fiddle with your OS/User seetings, try this for spanish messages:

java -Duser.country=ES -Duser.language=es

Hibernate Validator 5.1 Reference