I tested the following template and it did appear in e-mail invoices:
Code:
{* vim: set ts=2 sw=2 sts=2 et: *}
{**
* @ListChild (list="invoice.item.name", weight="20")
*}
<li style="list-style: none;line-height: 1.6em;color: #5a5a5a;">{t(#TEST LINE#)} Some text goes there</li>
Please check if you put the template in the right directory. You may also try to re-deploy the site once again.