wpml-config.xml

<!-- https://wpml.org/forums/topic/translate-wp-members-email-with-wpml/#post-482293 -->
<wpml-config>
    <admin-texts>
        <key name="wpmembers_email_newreg">
            <key name="subj" />
            <key name="body" />
        </key>
    </admin-texts>
</wpml-config>