Since no one seems to have a hint at hand, I have produced some (quick & dirty) code to perform this operation.

It's not universal, but it is quite straightforward and can be adapted easily to your needs. Its weak point is that it does not translate recursively "join"ed structures.

This code is not at all production-ready! as it does not cache locally the translations. A cache should be added to be ready for production.

  def translate(self, dataset, language_code, model):
    if self.__transcache == None: self._load_tcache()
    langset = self.__transcache[language_code][model]
    for i in dataset:
      id_ = i['id']
      for field in i:
#        print "Seeking field %s with ID %s" % (field, id_)
        if field in langset:
          sid_ = str(id_)
          if sid_ in langset[field]:
#            print "Found translation for %s[%s]:%s" % (model, field, id_)
            i[field] = langset[field][sid_]
    return dataset

  def _load_tcache(self):
    r = self.search_and_load('ir.translation', fields = ['lang', 'module', 'name', 'res_id', 'value'])
    l = {}
    for i in r:
      lng = i['lang']
      nam = i['name'].split(',')
      if (len(nam)<2): continue
      module = nam[0]
      field = nam[1]

      if not lng in l: l[lng] = {}
      if not module in l[lng]: l[lng][module] = {}
      if not field in l[lng][module]: l[lng][module][field] = {}
#      print "Added cache for %s[%s][%s][%s]: %s" % (lng, module, field, i['res_id'], unicode(i['value']).encode('utf-8'))
      l[lng][module][field][str(i['res_id'])] = i['value']
    self.__transcache = l