<class name="Child">
    <composite-id>
        <key-property name="parentId" column="parent_id"/>
        <key-property name="childId" column="child_id"/>
    </composite-id>
    <many-to-one name="parent" column="parent_id" insert="false" update="false"/>
...
</class>

<class name="com.xxx.model.District" table="district" schema="public">

        <id name="id" type="long">
            <column name="district_id"/>
            <generator class="sequence">
                <param name="sequence">xxx_guid</param>
            </generator>
        </id>

        <!--a district should have exactly one detail per language supported by the app-->
        <map name="details" table="district_detail" inverse="false" cascade="all,delete-orphan" fetch="join" >
            <cache usage="read-write"/>
            <key>
                <column name="district_detail_district_id_fk" not-null="true"/>
            </key>
            <map-key column="district_detail_locale" type="locale"/>
            <one-to-many class="com.xxx.model.DistrictDetail"/>
        </map>
    </class>

<class name="com.xxx.model.DistrictDetail" table="district_detail" schema="public">

        <composite-id name="id" class="com.xxx.model.DistrictDetailId">
            <key-property name="districtDetailDistrictIdFk" type="long">
                <column name="district_detail_district_id_fk"/>
            </key-property>
            <key-property name="districtDetailLocale" type="locale">
                <column name="district_detail_locale"/>
            </key-property>
        </composite-id>

        <many-to-one name="district" class="com.xxx.model.District" update="false" insert="false" fetch="join">
            <column name="district_detail_district_id_fk" not-null="true"/>
        </many-to-one>

        <property name="districtDetailName" type="string">
            <column name="district_detail_name" not-null="true"/>
        </property>

</class>

District district = new District();
       
        DistrictDetail detailZh = new DistrictDetail();
        detailZh.setId(new DistrictDetailId(district.getId(), Locale.PRC));
        detailZh.setDistrictDetailName("东城");

        DistrictDetail detailEn = new DistrictDetail();
        detailEn.setId(new DistrictDetailId(district.getId(), Locale.ENGLISH));
        detailEn.setDistrictDetailName("Dongcheng");

        district.addDetails(detailZh);
        district.addDetails(detailEn);

        mgr.saveEntity(district);

---part of District.java:
public void addDetails(DistrictDetail detail) {
        detail.setDistrict(this);
        this.getDetails().put(detail.getId().getDistrictDetailLocale(), detail);
    }