@MappedSuperclass
public abstract class AbstractEntity<ID> {

    public abstract ID getId();
}

@Entity
@Table(name = "USERS")
public class User extends AbstractEntity<Long> implements WithTranslationKey {

    @Id
    @GeneratedValue
    private Long id;

    private String name;

      /* boilerplate..... */
}

@MappedSuperclass
public abstract class AbstractTranslationEntity<T extends AbstractEntity<Long> & WithTranslationKey>
        extends AbstractEntity<Long> {

    @Id
    @GeneratedValue
    private Long id;

    @JoinColumn(name = "CLASSIFIER_ID", nullable = false)
    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    private T classifier;

    @Column(name = "LOCALE_CODE", length = 15, nullable = false)
    private String localeCode;

      /* boilerplate..... */
}

@Entity
@Table(name = "USER_TRANSLATION")
public class UserTranslation extends AbstractTranslationEntity<User> {

    private String translation;

    /* boilerplate..... */
}