social/mass_mailing_event/data/event_state_data.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2016 Antonio Espinosa <antonio.espinosa@tecnativa.com>
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<odoo>
<data>

<record id="event_draft" model="event.registration.state">
    <field name="name">Unconfirmed</field>
    <field name="code">draft</field>
</record>

<record id="event_cancel" model="event.registration.state">
    <field name="name">Cancelled</field>
    <field name="code">cancel</field>
</record>

<record id="event_open" model="event.registration.state">
    <field name="name">Confirmed</field>
    <field name="code">open</field>
</record>

<record id="event_done" model="event.registration.state">
    <field name="name">Attended</field>
    <field name="code">done</field>
</record>

</data>
</odoo>