Update translations for one specific lang

def update_lang(self,
                    lang: Optional[Text],
                    data: List[Tuple[Text, Text]],
                    flags: Flags):
        """
        Update translations for one specific lang
        """

        sd = SortingDict()

        for item in (self.parse_item(x[0], x[1], flags) for x in data):
            if item:
                sd.append(item)

        if lang not in self.dict:
            self.dict[lang] = {}

        d = self.dict[lang]

        for k, v in sd.extract().items():
            if k not in d:
                d[k] = SentenceGroup()

            d[k].update(v, flags)