This code returns a string in english:

description = (pool.get('ir.model.data')
               .get_object(cr,
                           uid,
                           'crm_unassigned_leads_notify',
                           'mt_unassigned_lead')
               .description)

However, it's translated to spanish in the module, and it appears correctly translated in the UI.

How can I get that string translated?

Note that I cannot use from openerp.tools import _ because this code runs as an automated action, in a sandboxed environment. See the whole code if you need to.