@Entity
public class Label implements Comparable<Label> {
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    private Long tid;

    @OneToMany
    @JoinTable
    private Map<Language,SynonymList> synonyms;
}

@Entity
public class SynonymList {
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    private Long tid;

    @OneToMany(cascade = CascadeType.PERSIST)
    private Set<LocalizedLabel> synonyms;
}

@Entity
public abstract class LocalizedLabel {
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    private Long tid;

    @Basic
    private String name;
    @Basic
    private String description;
    @Basic
    private Language language;
}

private final static String persistence_unit_name = "main_DB";
final EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistence_unit_name);
final EntityManager em = emf.createEntityManager();

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/persistence http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="main_DB" transaction-type="RESOURCE_LOCAL">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <shared-cache-mode>NONE</shared-cache-mode>
        <properties>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/my_DB"/>
            <property name="javax.persistence.jdbc.user" value="my_user"/>
            <property name="javax.persistence.jdbc.password" value="my_pwd"/>
            <property name="eclipselink.ddl-generation.output-mode" value="database"/>
            <property name="eclipselink.logging.level" value="INFO"/>
            <property name="eclipselink.logging.level.sql" value="INFO"/>
            <property name="javax.persistence.schema-generation.database.action" value="create"/>
            <property name="eclipselink.query-results-cache" value="false"/>
            <property name="eclipselink.refresh" value="true"/>
            <property name="eclipselink.cache.shared.default" value="false"/>
            <property name="eclipselink.cache.size.default" value="0"/>
            <property name="eclipselink.cache.type.default" value="None"/>
        </properties>
    </persistence-unit>
</persistence>