ZCML File
i18n.zcml

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:browser="http://namespaces.zope.org/browser"
    xmlns:i18n="http://namespaces.zope.org/i18n"
    i18n_domain="formtest"
    >
<browser:addform
    name="addfieldcontent.html"
    schema=".test_i18n.IFieldContent"
    permission="zope.Public"
    label="Add Field Content"
    content_factory=".test_i18n.FieldContent"
    />
<i18n:registerTranslations
    directory="locales"
    />
</configure>