Are you sure this is the best markup ? You are replacing the whole h2 (including the tags).
And what is form_title used for?
Not sure why you need that syntax, maybe you could just do
<h2 i18n:translate="" tal:content="view/manage_form_title">Title</h2>
That would probably not add it to your pot files, though. I think this has been discussed earlier here, try searching for it