'return the selection list (pairs (value, label)); labels are
translated according to context language'

def _description_selection(self, env):

    selection = self.selection
    if isinstance(selection, basestring):
        return getattr(env[self.model_name], selection)()
    if callable(selection):
        return selection(env[self.model_name])
    if env.lang:
        name = ('%s,%s' % (self.model_name, self.name))
        translate = partial(env['ir.translation']._get_source, name, 'selection', env.lang)
        return [(value, (translate(label) if label else label)) for (value, label) in selection]
    else:
        return selection
